# What is the Sandbox?

This "Sandbox" is a place where Code Golf users can get feedback on prospective challenges they wish to post to the main page. This is useful because writing a clear and fully specified challenge on the first try can be difficult. There is a much better chance of your challenge being well received if you post it in the Sandbox first.

See the Sandbox FAQ for more information on how to use the Sandbox.

## Get the Sandbox Viewer to view the sandbox more easily

To add an inline tag to a proposal use shortcut link syntax with a prefix: [tag:king-of-the-hill]

# Kaos Pendulum and Einstein's Revenge

The Double Pendulum system is a relatively simple system with quite complex behavior that's highly sensitive to initial conditions (i.e., "chaotic").

Doctor Kaos has designed a particularly fiendish double pendulum, using his diabolical machine "Einstein's Revenge". Einstein's Revenge is a device which couples matter and energy, causing the mass of the first pendulum (connected to the anchor point) to be a function of the energy of the second: m1 = sqrt(PE2**2 + KE2**2), with the potential energy measured from the rest position of the pendulum.

For this challenge, you must write a program or function to simulate a basic Kaos Pendulum, where the second pendulum has unit mass and both pendulums are unit length. It must accept the starting position of the Pendulum - two real numbers, theta1 and theta2 - as input or command-line arguments, and one positive integer equal to the number of seconds the pendulum will be active.

Your program must output the value of theta1 and theta2 for each second, either printing to stdout or returning as a list, or something similar.

## Notes

I don't know if this should be a golf, a popularity contest, or if there should be some scoring method for some other type of challenge.

# Blind (deterministic) Jenga

The idea for this came up in the chat room, under the broader topic of how to make a human dexterity game into a software KotH challenge. Here's the basic idea, which I don't think works, but I'd love to get feedback to make it better.

The jenga tower has three blocks per layer. Layers alternate between N/S aligned blocks and E/W aligned blocks.

There may be just two players, or more than two.

Each turn a player selects a block location to probe. If there's no block there, the player gets to go again. If there's a block there, it is removed from the stack. If this causes the tower to fall, the player loses. Otherwise, the block is placed in the next safe position at the top of the tower, unless all available positions are unsafe in which case the player loses. If the player has not lost, it is now the next player's turn. Continue until some player loses.

I think this won't work well because it will boil down to a relatively random competition between bots that start with edge pieces and bots that start with center pieces. I don't want to run the contest just to find out that that's the case. Maybe putting four blocks per layer would make that a non-issue. I'm open to other suggestions on how to make this challenge work.

A idea. Maybe I'll do it a long time later...

You have these options each turn (they need better names and a plausible background):

• Meet k If the bot k also did meet you, and nobody injects, both of your scores are increased by 1. Otherwise nothing happens. But if k is yourself, this is invalid and will be just like doing nothing.
• Invite k The bot k gets a notification that you are doing this, and in the next round, your output is ignored and you must do Meet k.
• Inspect k You will get these informations at the beginning of next round:
• What the bot k was doing.
• The score change of bot k.
• Who was inviting bot k.
• Who was trying to meet bot k. (This is not known by bot k if not inspecting himself and his score is not changed.)
• Who was inspecting bot k. (This is not known by bot k if not inspecting himself.)
• Who was injecting bot k (and another bot). (This is not known by bot k if not inspecting himself and his score is not changed.)
• Inject j k If j is meeting k and k is meeting j, your score is increased by 10 and their scores are both decreased by 1 instead. If one of them is pretending doing that, and the other is pretending or really doing that, your score doesn't change. Otherwise, your score is decreased by 10. They'll not know who is injecting unless they are inspecting you or self-inspecting instead.
• DoNothing Nothing happens.

Possible other options:

• Pretend action: action is any action other than Pretend. It's the same as doing nothing, but inspectors will be told that you are doing that action. The score change that the inspectors will see is calculated as if you really did that.
• Multiply: For each turn until the next time you meet some bot each other, the points you, the other bot and all the bots injecting you get are doubled (or incremented, I'm not sure).

Everybody can see only their own score, bots inviting them and the result from Inspect.

• I think that Pretend is a great action, and should definitely be included. – Nathan Merrill May 22 '15 at 19:30

# Is this a red-black tree?

A red-black tree is a binary search tree where each node has an additional 'colour' property, which can be black or red. The root and leaf nodes must be black, each red node must have black children, and the path from any node to any child leaves must have the same number of black nodes. For instance:

2B
|  \
1R  3B
|   |
~   ~


Is invalid because of a black violation (the path from the root to each leaf has a different number of blacks).

Your task is to determine whether a given tree is a valid Red-Black tree.

## Input

The input will be a string matching [ a-zA-Z]. A space represents a leaf, a lowercase character a black node, and an uppercase character a red node. The value of a node is the position in the alphabet: a is 0, b is 1, C is 2, and so on. The children of the node in position n are in positions 2n+1 and 2n+2. If the string ends before the position you're looking for, that node is a leaf. For instance, baD cf E corresponds to:

       1,B

/     \

0,B         3,R

/     \

2,B         5,B

/

4,R


## Output

Your program should output something other than whitespace on STDOUT if and only if the input represents a valid tree.

## Simple test cases

True      False
" "       ""        (Root black violation)
"a"       "A"       (Root black violation)
"dBeac"   "dBea"    (Black violation)
"dAE B"   (Red violation)


Question about extrapolating data from an incomplete tennis scoreboard

Introduction

It is a fine day at the Stack Exchange tennis club. The players have just finished playing a grand tennis tournament in a round robin style (every player plays every other player once). The final results were about to be announced when suddenly, the scoreboard explodes! It is a total disaster - now nobody knows what the final scores were! Luckily, a piece of the scoreboard is still intact. Can you write a program to figure out the rest of the scoreboard from only a small part of it?

If there are k players, our scoreboard would have had k*3 entries, indicating each player's wins, losses, and draws. It is presented in a list of space separated comma separated tuples. For instance, in a game with 4 players here is a possible final scoreboard:

0,2,1 3,0,0 1,1,1 1,2,0


In this example the first player did not win anything, lost twice, and drew once; the second player won all three of their matches; the third player won once, lost once, and drew once; and the fourth player won once and lost twice.

Input Description

As input, you are given a scoreboard similar to the one above, except some of the numbers have been replaced by ?. The ? indicate the numbers that were unrecoverable after the explosion. For instance:

?,?,1 0,?,0 ?,?,?


Output Description

Output the scoreboard, with the ?s replaced with the actual scores. The input scoreboard will always have enough information for you to deduce the final scoreboard.

For example, consider the above input. We know that the second player has 0 wins and 0 draws, therefore, they must have lost both of their games. The first player has a single draw, and since we know the first player beat the second player, that draw must be with the third player. Thus the output is:

1,0,1 0,2,0 1,0,1


Sample inputs and outputs

TODO: Sample inputs and outputs of higher k


Sandbox Questions

• I have an alternate formulation for this question where instead of an incomplete scoreboard, the complete scoreboard is given and the program has to generate a table of which player beat which player. Which challenge do you think would be more interesting?

Sudoku Swapping Shenanigans

Honestly, there's not many shenanigans in this challenge but I wanted that sweet tautogram title.

Introduction

Imagine you're on a train, and there is a Sudoku grid that's already been entirely filled in left on the seat. We'll represent this grid as a series of 81 comma separated integers from 1-9 on a single line. Each cell in the grid can be numbered as follows:

As with all Sudoku grids, there will be exactly 9 of each number present in the input.

The Sudoku grid will not be completed correctly. It will have the right number of each number, but they will be positioned wrong. Your program's task is to swap these numbers to solve the Sudoku puzzle correctly.

(Since your stop is next, you want to make this program solve the Sudoku puzzle as fast as possible.)

or:

(Since you're writing this program on a napkin, you want to make it use as little bytes as possible.)

Input Description

Input consists of 81 positive integers that are comma separated. Some of them will be prefixed with an X which means those are the ones that are already placed and you can't swap them.

Example input goes here.

Output Description

Output the swaps required to solve the grid in the fewest number of swaps. You should have a line for each swap, consisting of two numbers in the form:

a,b


where a and b are both different and in the range 0-80.

Here's an example output (and I haven't actually written the example input yet!)

80,0
8,9
14,15


So that would mean that to solve the grid we need to swap the number in position 80 with the number in position 0, the number in position 8 with the number in position 9, etc.

Sandbox Questions

• Are we trying to solve it in the fewest number of swaps, or just transform it into any solved sudoku grid (meaning I could swap every input into a single predetermined pattern)? – Geobits May 27 '15 at 16:11
• @Geobits Fewest number of steps. – absinthe May 27 '15 at 22:03
• Do you guarantee that the original clues give a unique solution? If so, there's a lot of overlap with existing Sudoku-solver questions, and fastest-code would need a very large and well-chosen set of test cases to be confident that it's not overly sensitive to the order in which heuristics are applied. The interesting (IMO) part of the question reduces to "Decompose a non-simple graph into cycles", and I think there may be better settings to present it. – Peter Taylor May 30 '15 at 13:40

Code golf challenge: Write a program or a function that solves the following problem. Normal code-golf rules apply.

Given a set of subnets, give the smallest possible network these can belong to. You should consider the network- and broadcast addresses in your calculations.

Example input:

128.208.0.0/18
128.208.128.0/17
128.208.96.0/19


Example output:

128.208.0.0/16


You might want to read up on IP prefixes before trying this.

# Flash Cards Viewer

In this challenge, your goal is to produce a flash card viewer. Since this is a Code Golf challenge, it won't be a particularly featureful flash card viewer - in fact, it'll be the bare minimum a flash card viewer can be. We'll implement the following features:

1. Reading a list of flash cards from a file;
2. Quizzing the user on either "side" of the flash cards;
3. Reporting to the user which ones they got incorrect.

Input Description

As feature number 1 suggests, for this challenge you must read input from a file (unfortunately, your language cannot participate if it does not support reading from a file). The file shall be called cards.txt and will be formatted as a simple list of values separated by a pipe character |. For instance, a "Family Names in Chinese" flash card deck might look like this:

Mother|妈妈
Father|爸爸
Elder Sister|姐姐
Younger Sister|妹妹
Older Brother|哥哥
Younger Brother|弟弟


Output Description

First, your program should ask the user which side of the cards they want to revise, using a user input function such as prompt() or raw_input(). An input of 0 indicates the user wants to revise the left side of the cards, and an input of 1 indicates the user wants to revise the right side of the cards. Use the message "Choose side:" when asking the user.

After that, the program will pick out random entries from the opposite side of the user's selection, and prompt the user to type in the entry's corresponding value. After the user has gone through the entire list, output the pairs that he or she got incorrect.

Here is an example of what a possible session might look like. What the user inputted in this example is signified with >.

Choose side:
>0

>Younger Sister

>Mother

>Father

>Younger Brother

>Older Brother
Older Brother|哥哥
Younger Brother|弟弟


# Fibonacci Box Packing Factory

### Introduction

The Electronic Goods Company is a company that produces electronic item of various sizes. They need to package their items in boxes so that they can be shipped off to the store. There are some restrictions regarding what item can be stored in what box:

1. Each box can only contain a single item, and each item can only be contained in one box;
2. The volume of the item cannot exceed the volume of the box;
3. If the volume of the item is exactly the volume of the box, the item can be placed in the box without any padding material required;
4. If the volume of the item is less than the volume of the box, then padding material equal to the difference of volumes must be placed in the box to prevent the item breaking.

For example, an item that had a volume of 2m3 could be placed in a box of volume 2m3 without any extra padding material, but if the same item was placed in a box of volume 5m3, we'd need to add padding material of 3m3.

The supplier company is called the Fibonacci Box Company, which supplies The Electronics Goods Company with N boxes and P metres squared of filling material. Each box's volume is determined by the Fibonacci sequence (so the first box's volume is 1, the second is also 1, the third is 2, the fourth is 3, the fifth is 5, etc.).

Your program goal is to figure out the minimum amount of padding material required to pack all of the electronic items.

### Input Description

Input is a space separated list of integers that indicate the volume in square metres of the electronic items.

//TODO: Example inputs and outputs


### Output Description

Output the minimum value of P required to fill all the boxes.

//TODO: Example inputs and outputs

• I'm assuming that items can't be split between multiple boxes, and that a box can't contain multiple items? – Nathan Merrill Jun 1 '15 at 4:03
• @NathanMerrill Yep. Rule 1 states only one item can be placed in each box. I'll edit for clarity. – absinthe Jun 1 '15 at 4:05
• A couple example would help understand the challenge. You could also add some explanation to them. E.g. 1 5 8 7 => 6 (N = 7, boxes = 1 1 2 3 5 8 13, used boxes = 1 5 8 13) if I understand it correctly. Volume is cubic metres, m3. – randomra Jun 1 '15 at 4:43

# NP Cops and Robbers

This is an idea I've had for a while, and I really want to get it to work, but there are some large hurdles.

Hurdle 1: I need to pick a puzzle, preferably one that is NP-Complete. I think lots of Nikoli puzzles are good candidates, and I am leaning towards Light Up

# Cops:

Cops will write a program to generate a puzzle. The puzzle has a maximum size of WxH. The cops must be able to generate the puzzle in under 1 second. Puzzles must be deterministic, but randomness is allowed as long as I can set the seed. The puzzles generated must have only 1 solution. The cop will post a sample puzzle in his post (for the robbers to use)

Your score is the shortest time any of the robbers solved your puzzle. Highest score wins.

# Robbers:

Robbers write programs to solve the puzzles. Robbers are not allowed to target the specific puzzles, but are allowed to target the specific algorithms used to generate the puzzle. If the cop were to change the sample puzzle posted, the robber should still be able to solve the new puzzle in a similar amount of time.

If you solve a puzzle faster than any other robber, your score increases by the time taken to solve that puzzle. Highest score wins.

Hurdle 2: How to measure time taken. I don't want to run all of the cops/robbers, especially if this becomes popular. I also don't want to use the GOLF framework, as that would take a really long time to run. So, possible I could have the person run som CPU-intesive algorithm on their computer, measure how long it takes, and scale all of their answers according to that time.

# Create a basic spell checker

In this challenge, you have to implement a basic spell checker. Your program will use the first input as a source.

## Specifications

• You will receive two inputs, one is a sentence/paragraph you use as a source for your spell checker, and the other includes wrong words (they can be correct too) which you have to correct using the first input.
• Possible mistakes: Missing one letter (e.g. helo), one extra letter (e.g. heello), substitution of one character (e.g. hilp instead of help), transposition of two adjacent characters (e.g. hlep instead of help).
• In other words, the mistake and the original word have to have a Damerau–Levenshtein distance of one.
• You can separate the inputs in any reasonable format. For example, instead of using a newline, you can use a pipe sign to separate them. (|) However, watch out so you don't use something like letters because they are used in the 1st input.
• It's possible for a word to have neither an identical word nor a word with 1 distance from the first input. You will have to leave them unchanged.
• You don't need to do anything with punctuation. That is, I won't test words that are followed by a punctuation. (E.g. From the first example, I won't ask the correction of 'blod')
• Challenge is case insensitive, both the input and output. Meaning that if 'The' is used in the 1st input and the 2nd input is 'teh' you can change it to 'The', 'teh', 'teH', and similar cases.
• If a word is in the first input, but also has a distance of 1 with one of the other words, do not correct it.
• If there are two words with the same distance, you can output either of them. (E.g. 'en' can change into 'on' and 'in' if the words are both in the first input.) You can also output both of them, but you'll have to use a slash between them. (E.g. 'en' can be corrected into 'in/on')
• You can assume words are just sequences of letters separated by spaces.
• You can use STDIN or the closest alternative in your language.
• Standard loophole rules apply.
• This is , so the shortest code wins.

## Examples

Input:

A criminal strain ran in his blood, which, instead of being modified, was increased and rendered infinitely more dangerous by his extraordinary mental powers.

increasd mnetal


Output:

increased mental


Input:

The fact is that upon his entrance I had instantly recognized the extreme personal danger in which I lay.

I recognizi dnger en


Output:

I recognize danger in

• There are several definitions of "distance". Since the most common one is probably Levenshtein, you might want to specifically say that original and mistake have to have Damerau–Levenshtein distance of one. Other questions: what is a word? Only sequences of letters? What about "doesn't" or "up-to-date"? (It's probably simplest to rule those out.) What do we output if there are two different words with distance one? E.g. does en become in or on if both are in the first string? – Martin Ender Jun 3 '15 at 20:33
• Is the input case insensitive? If so, is case of the output arbitrary too or do we have to preserve the input capitalisation? And are we guaranteed that every word in the second string has a word in the first string that is no more than distance 1 away? – Martin Ender Jun 3 '15 at 20:34
• @MartinBüttner I clarified it in the bullet point above it. Only transposition of adjacent letters, one missing letter, one extra letter and a wrong letter. I guess that's Damerau-Levenshtein distance. Regarding the two words problem, I guess you could output either of them. I'm not really sure about this. I'm open for ideas. – JNV Jun 4 '15 at 4:49
• @MartinBüttner Good point. It's case insensitive, and the output can be in any case. (e.g. If the first input includes 'The' and there's 'teh' in the second input, it should output 'the' or 'THE' or 'tHE' or ...). No, you're not guaranteed that there's a word with a distance of 1 in the first input. Take a look at the example #2, 'I' was not changed. Also, in your previous post, you asked what counts as a word. I already said it in the post 'You can assume all words in the 2nd input are separated by spaces.' I'll edit it for clarity. – JNV Jun 4 '15 at 4:56
• I was asking for distance "no more than 1 away". That is, could there be a word that has neither a word with distance 1 nor an identical word in the first input? "You can assume words are just sequences of letters separated by spaces." Yet in the first input, there is punctuation. What sort of punctuation should we expect? The rest looks good. – Martin Ender Jun 4 '15 at 12:43
• @MartinBüttner Yes, it's possible for a word to have neither an identical word nor a word with 1 distance from the 1st input. You can ignore the words that are followed by a punctuation, like blood in the 1st input. They won't be in the test cases. (E.g. I won't ask for the correction of 'blod') Thank you for your help. – JNV Jun 4 '15 at 13:10
• As for the 'lay' in the first example, I'll fix it now, thanks. – JNV Jun 4 '15 at 13:19
• Right, but the question is what do we do with words that have neither an identical word nor a word with 1 distance from the 1st input. Remove them? Leave them changed? Also, that second point might be worth mentioning in the spec. – Martin Ender Jun 4 '15 at 13:19
• @MartinBüttner Leave them unchanged. Thank you for your support. – JNV Jun 4 '15 at 13:26

# Multiply with restricted operations: Best lower bound

Multiply with restricted operations is a challenge to multiply two variables using as few as possible of four allowed operations: addition, reciprocal, negation, and variable assignment. The current best is 22 operations.

Your goal is to prove a lower bound L, a number for which you demonstrate that there are no solutions with fewer that L operations. The highest L wins.

You must explain why your code demonstrates the lower bound, and I must be able verify your code by running it. There is a time limit of 30 minutes. The natural approach is to search the space of possible solutions, perhaps shrinking it via mathematical arguments, but any method is allowed. Purely mathematical proofs without code are also valid.

Your code is limited to 30 minutes and 3GB of memory on my machine (Windows 7 with a Intel Core i5-460M processor). I may be satisfied with someone else running your code to confirm with a conservative adjustment for different machine speeds.

Your code needs to run on easily-available free software. Please include instructions on how to run your code.

The winner will be the highest lower-bound proven by [date]. Tiebreak is fastest runtime on my computer. I will give a bounty of 500 rep to the winner.

If your lower bound matches a solution, narrowing down the optimum to a single value, I will award you an additional bounty of 300 rep.

For Sandbox:

• I haven't done a fastest code before. Anything I'm missing? Any machine specs I should add?
• Maybe you should require the program to be able to prove lower bounds for arbitrary expressions, rather than only a*b. Otherwise, it will be impossible to tell if a brute-forcing program is doing anything correctly, for any bound too low to find an answer. – feersum Jun 8 '15 at 17:35
• @feersum I'd really like to let people optimize for just multiplication since that's the function I care about. Is it really impractical to verify that code is doing the search correctly if the user is required to give a detailed explanation of their method and why it works? I trust people to be honest as to what the code does. – xnor Jun 12 '15 at 17:49
• I do believe it is impractical. How can you really tell that someone is not randomly twiddling bits and then printing 19? It seems that (innocently) bugged answers are more likely than correct ones in an environment where there is no testing. – feersum Jun 12 '15 at 18:01

# Date-A-List!

### Introduction

The year is 20XX. Lists of integers are now members of society with a full set of rights. Like humans, lists like to have dates and get married. In this challenge, we'll produce a program "Date-A-List!" that will get as many lists as possible on happy and compatible dates. Lists tend to prefer using programs that use as little bytes as possible, so this program will be golfed.

Lists are compatible (that is, you can assign them to a date together) if they share 2 or more integers in the same order. For instance, the lists (1 2 3) and (2 3 5) would be compatible. The lists (1 2 3) and (3 2 5) would not be compatible because they do not share 2 or more integers that are in the same order.

Lists are also always monogamous -- they will never go on a date with more than one list. For instance, consider the lists (1 2 3), (2 3 5) and (5 1 2) -- although the first list is compatible with both of the others, it may only date one of them.

### Input Description

Input is a list of lists in brackets, space separated:

(1 2 3) (2 3 5) (5 1 2)


That input would indicate three lists to be assigned to dates: [1, 2, 3], [2, 3, 5], and [5, 1, 2].

### Output Description

If n is the maximum number of dates possible, output n lines, each line consisting of two space separated lists which are to be matched up. For instance, on the example input there are two possible outputs:

(1 2 3) (2 3 5)


or:

(1 2 3) (5 1 2)


[TODO: More complex inputs and outputs]

• It would be nice to include the word "matching" somewhere in the text, for searchability. It would also be nice to have the basic examples use slightly more variety: at present they're all 3-element lists which overlap on adjacent pairs, but neither of those are stated as constraints. How about using (1 2 3) and (2 5 4 3) as the example of compatibility? – Peter Taylor Jun 6 '15 at 13:43

# 5-a-side Toroidal Bot Soccer

## Randomised teams

This is a team game. Rather than being assigned permanently to one team or the other, each bot will play in a number of games, each for a different randomly composed team of 5 players ("5-a-side"), and score a point for each game in which its team wins. This means every game requires team work, but there is still a single overall winner after all games are played.

## Rules

There are no rules for the players (no referee, no penalties, no off-side rule). The movement of the ball defines the score and the players can do as they see fit.

### Scoring

There are no goal posts. If the ball moves off the right hand edge of the field, it reappears at the left hand edge of the field and team 1 scores a goal. Similarly team 2 score if it moves off the left hand edge and reappears at the right. The score will be represented by a single integer, that is increased by one when team 1 scores, and decreased by one when team 2 scores. At the end of a game, team 1 wins if the score is positive, team 2 wins if the score is negative, and a zero score is a draw/tie.

Movement over the top and bottom edges has no effect on the score.

The game lasts for 2000 time steps (each bot provides 2000 moves). If there is no winner by the end of the game it is extended by up to a further 1000 moves, with the game ending if either team scores.

## Physics

Physics is the main obstacle to real world toroidal soccer, and will not be respected in this game. The physics have been simplified as much as possible to hopefully allow games to be viewed live.

This is a non-contact sport. Bots pass straight through other bots (of either team) with no interaction. Each bot can only interact with the ball.

The playing field is a continuous rectangle of width 100 and height 50. The bots and the ball have radius 1. Bots and ball can move freely in any direction without meeting a boundary - the edges of the field wrap. The ball will rebound from any bot if their circumferences overlap.

### Turning and acceleration

Due to the use of simplified physics this is quick to explain:

A bot has a facing angle and a velocity. A constant acceleration applies in the direction specified by the facing angle. Drag is a deceleration proportional to the velocity (an acceleration in the opposite direction to the velocity, proportional to the size of the velocity). This means a bot that does not turn will accelerate to a maximum velocity where the drag matches the acceleration.

A bot can turn any angle instantaneously, but the velocity (and hence direction) will only change gradually. For example, a bot changing direction by 180 degrees will continue travelling backwards while it slows down to zero velocity, and then accelerate in its new direction.

The ball has no acceleration of its own, so other than collisions, its only change in velocity is due to drag. There is no spin.

### Collisions

Only the ball can be involved in a collision with a bot - bots pass straight through each other.

Although the radius of both bots and ball will be displayed visually as 1, I believe the results are the same if collision calculations are based on the bots having radius 2 and the ball being a point.

To keep calculation simple, the ball will be tested for collision with each bot by considering the bot to be a circle moving with constant velocity and the ball to be a point moving with constant velocity (that is, the acceleration will occur at instants, rather than continuously over time). Since this is also how the motion will be modelled generally, the collisions should be consistent with the motion of objects in the game.

This allows the exact point of collision to be calculated so the rebound can occur with no overlap.

## Communication

There is no communication between bots. Each bot communicates solely with the controller.

The communication method will depend on the controller type (language agnostic/specific). Players will either be functions/objects in a specific language, or separate programs that communicate through STDIN/STDOUT.

Each step all bots will be supplied with the same information, and will provide a facing angle which will be a float in the range [0, 360).

The information supplied to bots will be as follows.

• Team direction (1 for team 1 or -1 for team 2)
• Current score (positive if team 1 is winning, negative if team 2 is winning)
• Facing angle and velocity of itself
• Facing angle and velocity of 4 team mates
• Facing angle and velocity of 5 opponents

Facing angle will be given as a float. Velocity will be given as x and y components, so two floats.

The information will therefore be received as two integers followed by 15 floats.

# Sandbox questions

• Are any terms not familiar that would be worth linking or further explaining?
• Are there any further simplifications that could be made, without detracting from the game?
• Are any of the simplifications too much? Am I overlooking some way in which the game could become trivial?
• Is it correct to model the bots as radius 2 and the ball as a point? Does this give identical results to modelling the bots as radius 1 and the ball as radius 1?
• Are there any problems likely to arise from basing collision detection on constant velocity bots and ball? (Acceleration being applied instantaneously each step, rather than spread out over continuous time.)
• How long does each game last for? I like your idea of randomising the teams. How many bots are in each team? – euanjt Jun 16 '15 at 7:55
• @TheE The "5-a-side" in the title refers to 5 players per team - I wasn't sure how widely known that was so I'll edit that in. – trichoplax Jun 16 '15 at 12:41
• @TheE I'm not sure how long each game should last yet - I'll have to test with some example players once the controller is written. For now I'll say 2000 steps in order to have something that people can comment on. I guess it will depend on what acceleration and drag figures I settle on too - as that affects how far each bot can move per time step. – trichoplax Jun 16 '15 at 12:45
• If a player of the right team stays on the left part of the field, he could counter score every goal it's team take, right? – Katenkyo Jun 16 '15 at 13:26
• Yeah I didn't read the title :) oops – euanjt Jun 16 '15 at 14:00
• @TheE no problem - and thanks for the other feedback :) – trichoplax Jun 16 '15 at 15:17
• @Katenkyo all the players can move freely over the edges of the field, so if the left team can get the ball past the right team's players then it shouldn't matter which side of the field they are on. The left team can reappear at the left side of the field and keep kicking the ball further right. – trichoplax Jun 16 '15 at 16:06
• @Katenkyo also all players can see all other players, so a bot from team 1 kicking the ball past the right hand edge of the field can see any team 2 bots waiting at the left hand edge of the field. It can therefore aim to avoid them so they cannot simply kick it back. – trichoplax Jun 16 '15 at 16:08

# Build a Rorschach Generator

2 possible challenges:

## 1.

Help a poor struggling game dev write some code to quickly and efficiently generate a Rorschach inkblot.

Using your language of choice, generate a Rorschach inkblot. You may use any method of generating a random seed.

The generated image must be in black and white and reflect down the middle of the image. This is a code golf so the shortest submission will win.

OR

## 2.

Help a poor struggling game dev write some code to quickly and efficiently generate a Rorschach inkblot.

Given 2 input images (a source image and an image of a template inkblot), convert the first into the Rorschach inkblot of the second without changing the colours of the image.

You may assume that the images are the same size, however you may not display the original image unaltered. Anywhere in the template where the RGB values of the pixel are (255,255,255), you may not display the original image. The produced image must be vertically mirrored, so you will have 2 copies of the source image distorted and reflected in the result.

Then I'd provide source images some of which would probably be shamelessly stolen from either the Voroni Map or the Mona Lisa Colour Palette questions because those questions are awesome.

My thoughts:

I'm essentially hoping to get the source image in a twisted demented fragmented form, similar to if you gave a small child red cordial then the source image and a blur tool and said go nuts. I feel like my second challenge has potential, but I feel like I need to improve the challenge description and detail exactly what I want to be produced, but I'm not sure how to do that without a wall of text and without unnecessarily restricting the challenge.

• Your suggestions aren't code-golf. Code-golf means that the shortest code in byte/char wins. First of all, you should determine what will be the winning criterion. It will be hard to determine some if you want to keep it as a code-golf AND a pop-con. The first one is more designed to be a pop-con, as submissions can be creative. The second one is too restrictive to be a pop-con : for the same images, ouput will always be the same. It would go as a code-golf. Be aware that image-processing is language retrictive by essence, and that could be badly welcomed as a code-golf :) – Katenkyo Jun 23 '15 at 14:31
• Not necessarily a duplicate, but something to look over to make sure yours differs sufficiently Make a Rorschach image – trichoplax Jun 23 '15 at 16:48

# [Insert] Nerd Sniping Pattern (Series)

Having learned from Prime Nerd Sniping Pattern that hoping an optimal solution will not be spotted too quickly is not a good idea, I'd like to judge how much interest there is in a series of similar contests that have been demonstrated to not have an achievable optimal solution, allowing long term open ended competition.

Each one would need work to demonstrate this lack of an achievable optimal solution, and I'll put that work in if there is suffficient interest here.

For example, there could be a Fibonacci Nerd Sniping Pattern, Factorial Nerd Sniping Pattern, and so on. Each one would need to have a different method of defining the scoring pattern, so that different optimisation techniques and algorithms would be required for each one. This is what would ensure they are distinguished from each other as separate challenges in a series, rather than near duplicates.

# What I've learned from my mistake with the primes

The prime scoring pattern had a checkerboard optimal solution because all of the scoring pixels were on opposite coloured checkerboard squares to the pixel being scored. I need to avoid this in any future scoring patterns, and more generally avoid any pattern that divides the image into two regions for scoring (where all of one region are scored by combinations of pixels from the other). Intuitively, there should be plenty of mixing.

As I think about it more, I'll add ideas here on things to rule out and things to ensure I have before considering a pattern scoring rule ready for posting.

# Build a Mahjong AI

Mahjong is a traditional Chinese gambling game played throughout Asia in which four players draw and discard tiles in order to try to complete a hand of 14 tiles.

In this problem, a specification for a simplified version of Mahjong called "PPCG Mahjong" was given. Your task in this problem is to build a program that will play a version defined here called "Full PPCG Mahjong" (hereafter known as the FPM rules).

Your program will be an online program, taking input as it plays the game. (that does not necessarily mean it needs networking capabilities, but it means that it will output in reaction to ongoing input, not just all input at once.)

## Tiles

There are 34 types of tiles in FPM.

1. The “bǐng”/“pin” (餅) tiles, also known as the circle tiles / dot tiles. These will be represented in text with a number from 1 to 9 and then the letter b, as in 1b, 2b, up to 9b.

2. The “suǒ”/“sou” (索) tiles, also known as the bamboo tiles. These will be represented in text with a number from 1 to 9 and then the letter s, as in 1s, 2s, up to 9s.

3. The “wàn”/“man” (萬) tiles, also known as the character tiles. These will be represented in text with a number from 1 to 9 and then the letter w, as in 1w, 2w, up to 9w.

The three tile types totalling 27 tiles above are called the number tiles.

1. The “fēng”/”fuu” (風) tiles, also known as the wind tiles. There is one wind tile for each cardinal direction. These will be represented in text with the letter of the wind's cardinal direction in capitals, repeated twice, as in: EE, SS, WW, or NN.

2. The “yuán”/“gen” (元) tiles, also known as the dragon tiles. There is one red, one green, and one white dragon, represented as ZZ (for zhōng 中/center), FF (for 發/fortune), and BB (for bái 白/white) respectively.

The two tile types above are called the honour tiles. There are four of each type of tile, for a total of 136 tiles.

## Objective

The goal of Mahjong is to form a complete hand, which consists of four sets and a pair.

A set is one of:

• A sequence of number tiles. (e.g. 5w 6w 7w or 3s 4s 5s)

• A triplet of any tile (number or honour tile). (e.g. 3b 3b 3b or EE EE EE)

• A quadruplet of any tile. (e.g. 3b 3b 3b 3b or EE EE EE EE)

A complete hand will have 14 tiles if there are no quadruplets present; each quadruplet adds one tile to the hand's size, up to a possible 18.

## Gameplay

Mahjong is a game played in several hands (局, ).

At the beginning of each hand, each player receives a text input of START [Wind] [Round number]. Each player is then given an input of 13 tiles, represented as a set of 13 space-separated strings (e.g. 1b 9s BB 3w 6w 4b ZZ 3w 5w 2s 6b NN NN) and assigned a different seat wind depending on where they "sit" at the virtual table (given as a single letter out of NESW).

Starting with the player at position East and moving clockwise around the compass, each player takes a turn in which:

• The player whose turn it is will be given a tile (自摸牌, zìmōpái) from the "wall" (the collection of tiles that have not been drawn or dealt yet) as a two-character input.

• The player can take actions during the standby phase:

• If the player has four of the same tile in his hand, it can call kong (槓, gàng) and draw an extra tile. Those tiles must stay as a quadruplet from then on and cannot be used for anything else. The program does this by outputting kong [quadruplet tile] as text.

• If the player previously called pung on a triplet and has a fourth of the tile, it can call kong as well.

• If the player's hand is complete with this drawn tile, it may declare hu in which case the hand ends.

• The player will then produce an output of whatever tile it decides to discard. The tile that was discarded will be propagated as output to the other players in the form [seat] [discarded tile] (e.g. E 8w). The players can then call that tile if it will complete a set:

• The player immediately after the discarding player may call chi (吃, chī) by outputting chi as text during the call phase, to complete a sequence.

• Any other player can call pung (碰, pèng) to complete a triplet, similarly by outputting pung as text. Pung overrides chi when it happens.

• Any player can also call kong (槓, gàng) to complete a quadruplet, also by outputting text, in which case they are given an extra tile as text input.

• Any player can also call hu (胡, ) to complete their hand regardless of whether they are completing a sequence, triplet, or pair. Hu overrides both pung/kong and chi.

• If a player does not want to call tiles, it must output pass.

The turn immediately goes to the player who called the tile, and they skip their draw phase, discarding another tile immediately. If nobody called a tile, the next player draws one. At any point if a player calls, the other three players will receive an input indicating that the player in that seat made a call and what was called.

• For chi, the input will be in the form of [seat] chi [other two tiles] (e.g. S chi 6w 7w).

• For pung and kong, the input will be in the form of [seat] pung/kong. This is because all the tiles are identical to the called tile anyway.

• For hu, the input will be in the form of [seat] hu [all other tiles in hand].

In the above three cases, the tile being called is always the previously discarded tile.

• For a kong during the standby phase, the input will be in the form of [seat] kong [kong tile], because the kong tile is not implied to be the previously discarded tile.

• For a hu during the standby phase, the input will be in the form of [seat] hu [tile drawn]

Once a tile is called, the set that it makes is locked in place and cannot change for the rest of the hand. So if two tiles would make use of a tile in a called set, they may not use that tile.

A hand ends when either somebody calls hu validly or there are no more tiles to draw. (There is no dead wall in this game.) At that point, all players will receive an input of END to signal that the round has ended, and a summary of their points.

If somebody other than the dealer won, then the deal rotates. If the dealer or nobody won, then the deal stays the same. After four deal rotations, the prevailing wind also rotates.

A game of FPM consists of 16 such deal-rotations (rounds), such that each player gets to play one round with each combination of seat wind and table wind. Each player starts with a bank of 500 points. At the end of 16 rounds, the player with the most points is the winner of the game.

## Example gameplay interaction

> START HAND EAST 1
> 1b 4b 6b 2s 9s 3w 3w 5w 6w NN NN ZZ BB
> E       // The player is East (dealer)
> NN      // East drew the north-wind first.
BB        // East decides to discard the white-dragon.
> S 3w    // Nobody called it, and South discards a 3-character.
pung      // East wants to pung the 3w tile.
ZZ        // East discards the red-dragon
> S pung  // South pungs the red-dragon.
pass      // East has no use for this tile, so it passes.
> W kong 2s    // West declares a standby kong on 2-bamboo.
> W 3b    // West discards a 3-circle.
pass      // East passes again.
> N chi 2b 4b  // North chi-s it with a 2b and 4b.
> N 7s    // North discards a 7-bamboo.
pass
> 2w      // East's hand: 1b 4b 6b 2s 9s 2w 5w 6w NN NN NN -- 3w 3w 3w
2w        // East doesn't need the 2w, so he discards it.
> S hu 2b 3b 4b 7s 8s 9s 2w 6w 7w 8w ZZ ZZ ZZ
// South wins on that tile. The 2w completed his pair.
> END
> 496 506 499 499  // Their current point counts. South's hand was worth
// 2 points, so East pays 4 while the others pay 1.
> START EAST 2
> [13 more tiles]
> N       // The deal rotated, and this player is now North.


## Brackets

Your program can participate in one of three levels of gameplay:

• Level 1, where every hand is worth exactly 8 points, and the only thing that matters is completing hands.

• Level 2, where every hand is worth the number of points in the points table section below, but any hand can still win.

• Level 3, where every hand is worth the number of points in the points table, but a hand must have at least 8 points total with that system to win.

(TBD)

## Penalties

The following are invalid moves:

• Failing to produce an output when required.

• Discarding a tile that is not in your hand, or when it is not your turn.

• Calling chi on any player other than the one immediately before you, or calling any tile that does not actually complete a set in your hand.

• Calling hu when your hand is not complete, or when your hand value does not meet the minimum point requirement in level 3 gameplay.

If your program makes an invalid move, the move will be rejected, your program will pay 20 points to each of the three other players, and for the rest of that round, it will be a "forced tsumogiri" player, which automatically discards every tile it draws and never calls anything.

## Special Rules

There are no special rules such as dora or furiten in FPM. Any person may complete a hand at any time as long as it is a valid complete hand.

• Sounds fun :) I hope there'll be enough entries to actually play a game though – Sp3000 Jun 24 '15 at 4:34

# Team Gun Battle

This is an individual competition, where the goal is to be the last player surviving. Fighting always takes place between two teams. At the beginning, every player is randomly assigned to one of two teams and placed randomly on the board.*

Each turn, a player can move north, south, east or west or stay. In addition to moving, they can also shoot a bullet north, south, east, or west. Note that players won't know about other players' movements when they move, but the shoot() method is called after all moving has taken place. The player can choose to shoot a light bullet, which travels 4 squares per frame and does 1 damage, or a heavy bullet, which travels 2 squares per frame and does 3 damage. The bullets do move on the same step they were shot in, so if a target is less than 4 units away, you can shoot a light bullet without any chance of the target dodging.

Every player has a starting health of 30 and 30 bullets to shoot.

After 1000** or so steps, the round will end. Whichever team has more players alive will be considered the winners. Ties will be broken by whichever team has the highest total health.*** Every player not on the winning team will die, and the winning team will be split up into two new teams. This means that half of those who were originally on your side are now your enemies. Another 1000 steps are executed and another winning team is chosen. This process repeats until there is only one player left.

This has some interesting strategic consequences. For example, if your team is winning, it is in your interest to start shooting players on your own team because they may not expect it and you will have to fight them eventually. Similarly, you don't want to waste all of your bullets on the first few rounds because your bullets and your health is not replenished after each round. I like trichoplax's suggestion where ammunition and health could be slightly restored after each round. You want to get your teammates to do as much work as possible before killing them.

The controller almost ready. This is the spec:

public class Player1 extends Player {
public Direction move(World w, int stepsLeft) {
// stepsLeft = # of steps left in round
// List of players: w.getPlayers()
// List of bullets: w.getBullets()
Player p1 = w.getPlayers().get(0);
// Check health: p1.getHealth()
// Check # of bullets left: p1.getBullets()
// Check team: p1.isOnSameTeam(this)
// Check position: p1.getPosition()
return Direction.NORTH; // always move north
}
public Bullet shoot(World w, int stepsLeft) {
// similar to above
return new Bullet(Direction.NORTH, true); // heavy bullet shot north
}
}


*I think the board should be a square with side length 3*(# of players). Hopefully this would make to not too sparsely populated.

**Exact number to be determined. It may be based on the number of players (higher # of players = more steps until the end of the round). 1000 seems like a good number.

*** I'm working on a system that's somewhat more fair. Currently, if there was originally an odd number of players, they were split with one random team getting an extra player. Obviously, that team has a significant advantage under this system. Perhaps it could be percentage of surviving players?

• It sounds like it would be easy to forever avoid opponents by just staying off their orthogonal lines. What happens if it never gets down to one player for that reason (or everyone runs out of bullets)? – Geobits Jun 25 '15 at 16:37
• @Geobits If everyone runs out of bullets, then I have two options I'm considering: a) Nothing happens, and when the 1000 frames ends at the end of the round, one team is randomly chosen to proceed (that is the default when teams tie exactly; if one team has higher total health than the other, then that team wins) b) everyone's bullets are replenished. Which is better? – soktinpk Jun 25 '15 at 17:06
• Would it help to give everyone some extra ammunition at the start of each round, but also let them carry over whatever ammunition they saved from the last round? – trichoplax Jun 25 '15 at 17:21
• If you were feeling mean you could make the arena wrap and have bullets not stop until they hit someone. So dodged bullets will keep looping across the arena, slowly filling it up until there's no way for everyone to avoid them. – trichoplax Jun 25 '15 at 17:22
• @trichoplax I like your first idea. The second seems like a little harsh since you have a lot less control of who your bullets hit. – soktinpk Jun 25 '15 at 17:30
• I did think it might be a little too mean :) – trichoplax Jun 25 '15 at 17:31
• If everyone runs out of bullets, then there is obviously a knife fight. – feersum Jun 25 '15 at 21:40

A few minutes ago, I posted this question as a popularity-contest which was quickly put on hold as too broad. Specifically, the "there are no restrictions on what the programs/functions do" was apparently not quite right. A commenter also suggested that an empty program would be a possible answer which I knew, but didn't necessarily want to restrict as I think the popularity contest would have taken care of that. I'd be interested in any suggestions people have to make the question more appropriate for PPCG.

Also, I plan on asking with the tags popularity-contest and restricted-source. Does that seem right?

Here is the question:

Inspired by the bonus in this question

Write some code that can be run in multiple directions. In each direction, the code must be a complete program or a function. The code must be written in one language (so for example, you cannot have a python program that is also a whitespace program when run backwards).

### Explanation of "multiple directions"

abcd efgh
ijklm
nop


Then backwards is

hgfe dcba
mlkji
pon


And sideways is

a n
bio
cjp
dk
l
em
f
g
h


### Trivial example

Brainfuck

 .
.+++++++++
+++++++++
+++++++++
+++++++++
+++++++++
+++++++++
+++++++++
+++++++++
+++++++++.
.


### Notes

• there are no restrictions on what the functions/programs do
• your code must be able to run in at least two directions, but more is better
• abuse of comments is frowned upon but allowed
• Welcome to the sandbox! You deleted your post before I could add another comment, so here's what I wanted to say: What makes an answer "good" in this question? If we go by the criteria "your code must be able to run in at least two directions, but more is better", which the empty program satisfies, that seems a little contradictory. Thus I think it's good to place some sort of restriction on the programs. I think source-layout is better than restricted-source - take a look at the questions there and see what you think :) – Sp3000 Jun 27 '15 at 6:17
• Also, as is even if the question wasn't closed as too broad, it'd probably be closed as a duplicate of this question, which you might want to also take a look at. – Sp3000 Jun 27 '15 at 6:18
• Thanks, I'll look through those questions. And I think you're right. That other question is pretty similar. I might just let it go. – sudo rm -rf slash Jun 27 '15 at 13:40

### Allongiator code-golf

There are a lot of acronyms on the internet -- ROTFL, RTFM, NSA, laser, taser, and so on. Your job is to write code that, given an acronym, can figure out what that acronym might stand for. You'll be given an alphabetically-sorted list of words that you can use, to be provided in the format of your choice.

Note that if you're given an actual acronym, you don't have to provide what it really stands for. As an example, given ROTFL, you could output "rolling on the floor laughing", or you could output "rearrange orange thrice free language".

### Input

1. A dictionary of all of the words you're allowed to use. This is guaranteed to have at least one word for each letter; your program is allowed to do anything it wants if it encounters a letter that it can't find a word for.
• Not necessarily in alphabetical order
• All in lowercase
2. A string of lowercase letters, with no whitespace, punctuation, or non-letter characters.

They can be given in any format you want. For example, the acronym could be the first command line argument and the dictionary the rest of them, or they could be arguments to a function, or given via standard input, or whatever.

The dictionary contents can be found [here].

### Output

1. A string containing a space-delimited list of words that form the acronym given as input, from the dictionary given.
• No trailing whitespace except for a single optional newline
• The words must be chosen (pseudo-)randomly from the dictionary -- that is, if I run it twice with identical inputs, I should get different outputs1.
• It doesn't have to make sense or be plausible or grammatically correct. Any words that start with the right letters will do; however, bonus points2 to anyone who manages that.

Since this is , the shortest answer wins.

All the standard prohibitions apply here, though with the note that accessing the dictionary from the web is acceptable, so long as it's the unmodified dictionary and nothing else.

1: Barring practically impossible situations.
2: That is, a browser cookie

Sandbox (foot)notes:

This may very well be a duplicate. I looked around as much as I could, but I don't even know what this is called, so I didn't find much. Apologies if it is.

Would they be acronyms or initialisms? I'm not sure.

I'll add the actual dictionary once I've found a nice one that isn't massive.

• A quick search for acronyms turned up this – Sp3000 Jun 27 '15 at 6:31
• @Sp3000 ...I even upvoted that question and I forgot about it. Should I delete this post? – Fund Monica's Lawsuit Jun 27 '15 at 6:32
• I'm not sure tbh... might be good to get a second opinion, since I'm not sure whether that one being a popcon changes anything – Sp3000 Jun 27 '15 at 6:33
• @Sp3000 Alrighty. I'll leave this up. (Thanks for replying so quickly, by the way) – Fund Monica's Lawsuit Jun 27 '15 at 6:51
• Eww, CR..... =) – Faraz Masroor Jun 28 '15 at 3:42
• @FarazMasroor Nooo my secret is revealed (I recognize you from that meta question! Hi!) – Fund Monica's Lawsuit Jun 28 '15 at 3:42

## Introduction

You're fed up. You've tried to sell your car but failed, not knowing whether your price is too high, too low or people are just too picky. Then a programmer decides to take a look at your car and makes you an offer using a program that he had written for judging a car's worth.

## Challenge

Given a car's make, model and mileage, you have to find how much a car is worth using the method below. The shortest program to do so wins.

If the make or model of the car is incorrect, you must output "Error: [input make/model] is invalid".

## Method

First of all, you should scrape all of the prices and mileages of all of the listings on AutoTrader.com of the specified car. Next, plot these on a graph (this graph is not needed to be shown) of mileage against prices.

On the graph you should draw a line of best fit. Now you can read the price on the line of best fit for the specified mileage of the car. Now output this with a dollar sign before the price.

## Example

None of these prices are correct output

Ford Fiesta, 200 miles

Input: ford, fiesta, 200
Output: $15000  Subaru Outback, 0 miles Input: subaru, outback, 0 Output:$27000


## Example script

Here's my example test script in Python 2.7 (uses autotrader.co.uk though, not .com):

from BeautifulSoup import BeautifulSoup
import urllib2, sys, re, pylab

model, make, mileage, postcode = sys.argv[1:]
mileage = int(mileage)

soup = BeautifulSoup(page)

results = soup.findAll("div", {"class":"search-result__content"})

cars = []

for j in results:
pricetag = j.findAll(text=re.compile(r"&pound;.*"))
price = int(pricetag[0].replace(',','').replace('&pound;',''))

mileages = j.findAll(text=re.compile(r".+ miles"))
mileagecar = int(mileages[1].replace(" miles","").replace(",",""))

cars.append([mileagecar, price])

x = [k[0] for k in cars]
y = [i[1] for i in cars]

poly = pylab.polyfit(x, y, 2)

print("£"+str(int(pylab.poly1d(poly)(mileage)+0.5)))

• I believe scraping autotrader.com violates their visitor agreement. Section 5 seems to imply that it's illegal as well (though that may well depend on the jurisdiction). – Geobits Jul 1 '15 at 20:00
• @Geobits Damn it haha... I'll look for some kind of API for another online car sales site... – Beta Decay Jul 1 '15 at 20:01
• I'm also not sure where the pounds/dollars difference comes in. Both of those cars are available in the US, for example, but output is in pounds. I don't see anything in the input to say which to use. – Geobits Jul 1 '15 at 20:05
• @Geobits It was based on whether the program used AutoTrader**.com** or .co.uk – Beta Decay Jul 1 '15 at 20:07
• Well... I mean I got that. But it's a code golf; why would you use the longer one? I assumed there had to be some reason you made the choice, not just because you felt patriotic ;) – Geobits Jul 1 '15 at 20:09
• For instance, what if I decide to use the US site, and there are no matches for a particular make/model (even if there may be on the UK site)? Is my output "wrong"? – Geobits Jul 1 '15 at 20:10
• @Geobits I see... Well I'll limit it to an American site when/if I find one – Beta Decay Jul 1 '15 at 20:14
• Doesn't really matter where the site is from, really, as long as it's one site. Or there's something in the input to determine that. If the input was, say ford fiesta 200 dollars (or us/uk, gbp/usd, etc) then that part wouldn't be an issue. – Geobits Jul 1 '15 at 20:15

# Meta-Manufactoria

Manufactoria is a pretty great programming game. However, instead of writing machines to solve the problems, your goal is to write a program that creates the machines for you. If you are already familiar with Manufactoria, then for the next section, you only need to read the italicized phrases.

# The Rules of Manufactoria

In this version of Manufactoria, you are placed in a 9x9 world. The input generator is in the center top square (4, 0), and the output acceptor is in the center bottom square (4, 8). When input is generated, it moves immediately down.

Input is represented by a robot that has a queue of colors. Output will be the same robot, but the queue may contain a different sequence of colors. Robots must always eventually end up in the output square. There are 2 colors available, Red and Blue.

Each tick, the robot moves 1 square. The direction the robot moves, and any modifications to the queue is determined by the square it is on. There are 3 types of squares:

1. Movement square. This square either moves the robot North, East, South, or West and does not affect the queue. You cannot have two movement squares on the same tile

2. Choice square. This square moves the robot based on the top color in the queue. The general Choice square moves the robot east if red, west if blue, south if empty, and never north. This square can be rotated or reflected to change the directions traveled.

3. Writer square. This square writes a color to the back of the queue, and moves the robot in a given direction.

# STDIO and Scoring

Your program will be passed two lists of the same length, one containing the inputs, and the other containing the outputs. Each item of each list contains only the R and B characters, representing the input queue.

Your output is the board that solves the Manufactoria puzzle. Each square is represented by two characters. The first character represents the square type, the second represents the direction. The square types can be:

• Movement
• Choice
• Red writer
• Blue writer.
• .. Empty square
• II Input
• OO Output

The directions are: - North - East - South - West.

The direction listed for a choice tile represents the direction traveled if the queue is empty. If the direction is lowercase, the tile is reflected (which swaps the colors).

The program which solves more puzzles than any other program wins. In the event of a tie, the tiebreaker is the program that produces the most efficient solutions. Efficiency is measured by the number of times the robot moves across all of the solutions.

Your program should be a general solver. I may add puzzles to the ones listed below at any time.

# Sample Puzzles

The solutions given below don't necessarily have to do what the title indicates. Your program's solution also doesn't have to match the ones listed below. It only needs to solve the inputs given. The format below is

[Inputs] [Outputs]
Solution Map


Example 1: Don't do anything

["","R","B","RRBR","BRRBRB"] ["","R","B","RRBR","BRRBRB"]

........II........
........MS........
........MS........
........MS........
........MS........
........MS........
........MS........
........MS........
........OO........


Example 2: Print second R and anything after:

["","R","B","RR","BRB","RBRBBB"] ["","","","R","","RBBB"]

........II........
..MSCSMWCSMW......
..RSMEMEMS........
BECsMEMEMS........
........MS........
........MS........
........MS........
........MS........
........OO........


Example 3: Reverse String (This doesn't reverse any string, it only works for the examples listed)

["","BBR","B","RRB","BRRRB","BBRB"] ["","RBB","B","BRR","BRRRB","BRBB"]

........IICsMERS..
......CECSCEMSBS..
......RSMSCEMSMW..
......REMSCEMS....
........MSRSMS....
........MSRSMS....
........MSRSMS....
........MSBWMW....
........OO........


Example 4: Only include Rs

["R","","BBR","BRR","B","RBRBRBBR","BBBBBBRRR","RBBBRBRBBB","RRRR"] ["R","","R","RR","","RRRR","RRR","RRR","RRRR"]

........II........
........MEMEMEMS..
MSCSMWCSMWCSMWCSMW
REREMERERSMW..MS..
........MSMWMWMW..
........MS........
........MS........
........MS........
........OO........


• Sounds extremely difficult. – feersum Jul 7 '15 at 3:07
• I enjoyed playing that game...Hard indeed. :-) – Spikatrix Jul 7 '15 at 12:39

(Need a title.)

Write two programs (or functions) in the same language for these two tasks:

1. Given a list of integers, split at every non-negative integer. If there are two or more consecutive non-negative integers, your program should preserve the empty list between them.
2. Given a list of lists of negative integers, concatenate the lists and insert non-negative integers between them. The inserted integer after the nth list (zero-based) should be n.

Alternatively, you can increment every integer by one for both tasks. So you split at positive integers, accept non-positive integers in task 2 and the inserted integers start at 1.

The input for task 1 and the output for task 2 should have the same format, with the exception that one can be the string representation of the other in your programming language. The same goes for the output for task 1 and the input for task 2.

Your score is the total length of your two programs times (30 + their Levenshtein distance). Lowest score wins.

Input:  [-5 7 8 -5 2 -6 -3 -3 8]
Output: [[-5] [] [-5] [-6 -3 -3] []]


Input:  [[-5] [] [-5] [-6 -3 -3] []]
Output: [-5 0 1 -5 2 -6 -3 -3 3]

• if(1>2){code1}else{code2}. There's no need to ever have the edit distance any greater than 1 or 2. – John Dvorak Jul 12 '15 at 6:03
• better yet: if(input[0] instanceof Array<int>){code1}else{code2}. Haskell might be able to pull this off even more cleanly because the typeclasses are resolved at compile time, meaning that even empty arrays have the proper type. – John Dvorak Jul 12 '15 at 6:06
• The first task description is extremely unclear. What does it mean to split? How can one preserve something that didn't exist in the first place? – Peter Taylor Jul 12 '15 at 16:55
• @JanDvorak If the answer is less than 30 bytes, it is beneficial to remove a byte while increase the edit distance by one. But maybe I should change it to the length plus the edit distance. – jimmy23013 Jul 12 '15 at 19:48
• @PeterTaylor It just works like the CJam and GolfScript /. I'll try to reword it later if I get the scoring method working. – jimmy23013 Jul 12 '15 at 19:50

# Return of the 5318008

## Introduction

A week or so ago, I posted the challenge 5318008, with a massive reaction. Now, I want you to do the same again but with musical chords.

## Challenge

Given a word list, you must output a list of words which can be formed using musical chords. However, the word must also sound good too.

The chords which you may use are:

A B C D E F G


These are all the major chords without the flat/sharp chords.

A word will sound good if all of its letters are within the same key. All the chord progressions which you must concern are listed below:

• A major: A D E G
• B minor: D G A
• D major: D G A
• E major: E A B D

Other progressions such as G or C major could not make any word because all of the major chords (which were not sharps or flats) were consonants.

For my tests, I used the UNIX wordlist, gathered by typing:

ln -s /usr/dict/words w.txt


Or alternatively, get it here.

There are some uppercase letters in the dictionary, so make all of the letters in all of the words in the dictionary lowercase.

## Winning

The shortest code to output a list of words wins.

• What about A minor? – Nathan Merrill Jul 13 '15 at 17:03
• @NathanMerrill No vowels in Am, just C F and G – Beta Decay Jul 13 '15 at 17:05
• I don't understand then. A minor includes "a" and "e" – Nathan Merrill Jul 13 '15 at 17:09
• What about case sensitivity? Also I'm expecting this to end up as a regex challenge, if I've understood the problem correctly – Sp3000 Jul 13 '15 at 17:10
• @Sp3000 Edited to say that all words should be converted to lowercase – Beta Decay Jul 13 '15 at 17:13
• @Nathan Sorry, I was talking about chords instead of notes :/ – Beta Decay Jul 13 '15 at 17:14
• So I'm to assume that A would only be included if A major is a subset of the key? – Nathan Merrill Jul 13 '15 at 17:18
• @Nathan Uhh yes – Beta Decay Jul 13 '15 at 17:22
• Ok. Also, B minor and D major include the same notes, so the notes listed should be the same. D major shouldn't have the C, as it has a C#. – Nathan Merrill Jul 13 '15 at 17:24
• I don't know much about music theory, but from what little I do know I find this question very confusing. A B C D E F G doesn't look like a list of chords, but like the scale of C major. If by the "key of C major" you mean the tonic chord of the scale of C major, that would be C E G, which is not all consonants. I also promise to downvote any question which allows people from one specified nation to answer a different question to people from the rest of the world. – Peter Taylor Jul 13 '15 at 19:25
• @PeterTaylor Refer to this: The chord chart...lists all the common traids and four note extended chords belonging to the key of C major. – Beta Decay Jul 13 '15 at 19:35
• Yes, but that doesn't clear anything up. Unless... are you sure you're not confusing chords with chord progressions? – Peter Taylor Jul 13 '15 at 20:55
• @PeterTaylor Yes, that's exactly what I meant. I didn't know the word for it – Beta Decay Jul 13 '15 at 20:58
• You are definitely confusing notes and chords here. B minor and D major both contain the notes B C# D E F# G A, The possible chords are Bm Em F#m Dmaj Gmaj Amaj and C#dim, with F#m and Em often subsituted for Fmaj and Emaj. One valid interepretation is that both keys contain all these chords, another is that the minor is just B E (F#) and the major is just D G A. Under no circumstance can Bm be considered D G A. You are also misusing the word progression. This refers to the sequence of chords in a particular song and has nothing to do with the chords available in a particular key. – Level River St Aug 8 '15 at 12:32
• A major contains A B C# D E F# G# so the only natural notes are ABDE,which is what you have written for E major. E major contains one additional sharp E F# G# A B C# D# so the only natural notes are E A B. – Level River St Aug 8 '15 at 12:35

# Break out of the digital world!

Note: The tag is just something I knocked up quickly, if anyone has any better ideas please let me know.

## Challenge

You must write a morse code to ASCII translator using an external device (such as a button or the spacebar on the keyboard).

### Dots

A button press is a dot when it has been pressed for 0.5 seconds or longer and released.

### Dashes

A button press is a dash when it has been pressed for 1 second or longer and released.

### Exit

A button press is an exit when it has been pressed for 5 seconds or more. This should end the program and display the result.

### Space

A space is when there has been no button input for 1 second. This should move on to the next letter.

Your code should support every character on the following:

http://zunkworks.com/images/bluetoothmorse/morsecode1.gif

## Winning

The shortest code wins. You may write this in any language that allows input from an external source. For example, Arduino or Python (on a Raspberry Pi).

• Does this actually have to be able take input from hardware? Can you allow feeding in simulating data? I think a standard format like a sequence of numbers measuring current/voltage every millisecond would make it more accessible. – xnor Nov 18 '14 at 1:35
• While I do own an arduino, I see absolutely no reason why this challenge should be limited to using an external switch. Is there anything wrong with using the space bar or a mouse button? If it HAS to be an external switch, how about I rip open my mouse and connect an old doorbell push across one of the mouse button contacts? – Level River St Nov 27 '14 at 20:45

# VSEPR Strikes Back!

(Note: I know that the VSEPR method fails sometimes, and that there are exceptional molecules. This is addressed in the scoring system, and otherwise the challenge is about the molecules which conform.)

Most people who have taken an introductory chemistry course know about molecules, and (probably) the VSEPR theory of chemical bonding. Basically, the theory predicts the shape of a molecule given three main properties: the central atom A, the number of atoms bonded to the central atom X, and the number of lone electron pairs E on the central atom. Applying the VSEPR theory is simply a matter of finding the values of X and E (A always has an implied value of 1, as we'll see). This is called the AXE method. For example, a molecule which has 1 lone pair and 3 atoms bonded to the main atom is AX3E1, which is the trigonal pyramidal configuration.

## The Challenge

Your job is, given a covalent chemical compound, to output the geometrical shape of the molecule inputted. But wait! exclaim the exasperated programmers, you can't expect us to input all of the molecular data for every element! Of course we can, but I'm not feeling particularly masochistic today, so born was the scoring system below.

The input is any molecule, such as CO2 or HgCl2, and the output should be the name of the shape and NOT the AXE form. Ions should have their charge put in parenthesis directly after the ion, such as CO3(2-) or NH4(1+). 1- and - (and 1+ and +) are all acceptable.

## About the central atom A

In most cases, the central atom will be apparent. It usually has no subscript in the chemical formula: the C in CO2 is the central atom, for example. In a few cases, though, you might face compounds like ethelyne (C2O4), in which no clear atom is the central one. In this case, it is worth noting that such compounds are usually symmetrical, and considering any carbon to be the central atom will do.

## Scoring System

The base score is the number of bytes the program takes.

1. There is a minimum of 6 elements to be implemented for input; every 5 extra you add multiplies your score by 0.9.
2. Multiply your score by 0.8 if you can make your code work for ions.
3. Multiply your score by 0.9 if you can detect ionic compounds (VSEPR only works for covalent compounds) and reject them accordingly.
4. Multiply your score by 0.8 if you also output the bond angles.
5. There are certain classes of molecules which VSEPR fails to predict correctly, due to various reasons. (Check the first link in the post for the section on the exceptions.) Multiply your code by 0.9 per class if it returns those correctly.

## Test Cases

The parts in brackets are optional bonuses from above.

CO2: CO2 -> linear [180*]
HgCl2: HgCl2 -> linear [180*]
H2O: H2O -> bent [104.5*]
[CO32-: CO3(2-) -> trigonal planar 120*]
BrF: BrF3 -> T-shaped [90*]
[NaCl: NaCl -> Ionic compound]
XeF4: XeF4 -> square planar [90*]

Notes:
- The bonding patterns are not valid when the central atom is a transition metal (so don't do that.).
- Standard loopholes apply.

# One transparent colour sprite

## Overview

This challenge will only involve a hex string as input and a hex string as output, but will be explained in terms of computer graphics.

Given a fixed size background image, a smaller fixed size sprite image and its location, place the sprite on the background image allowing the background to show through for one specified colour of the sprite image.

## Details

• The background image will always be 32 by 18 pixels.
• The sprite image will always be 8 by 8 pixels.
• The colours will always be in the range 0 to 3 inclusive.
• There will always be exactly one transparent colour, from 0 to 3 inclusive.
• The location (x, y) of the sprite may be outside or partially outside the background image.

## Input

Since all inputs will always be the same size, there will be no separators, just a single string of hex digits.

To avoid having to define negative inputs, the top left pixel of the background image will be (128, 128), increasing left and down, and x and y will be defined by 2 hex digits each, giving a range of 0 to 255.

The input hex string will be made up of:

• Background pixels, 2 per hex digit, a string of 32 * 18 * 0.5 = 288
• Sprite pixels, 2 per hex digit, a string of 8 * 8 * 0.5 = 32
• Transparent colour, a single hex digit (the most significant half of the hex digit is unused)
• Sprite x and y, 2 hex digits each, a string of 2 * 2 = 4

The input will therefore be a string of 288 + 32 + 1 + 4 = 325 hex digits with no separators.

## Output

The output is the finished 32 by 18 pixel image, as a string of 288 hex digits with no separators.

## Format

### Pixel order

Each image is ordered in English reading order, left to right then top to bottom. That is, the pixels are listed in rows. The first pixel listed will be the top left. This applies to both the background image and the sprite image.

### Colour encoding

Pixel colours are encoded 2 per hex digit, most significant first.

For example, the hex digit B corresponds to binary 1011. This means the first pixel has value 10 = 2 and the second pixel has value 11 = 3.

### Transparent colour

Since the single transparent colour is encoded in one hex digit, which normally holds 2 colours, the first 2 bits (most significant) are ignored and the last 2 bits (least significant) are used to represent the transparent colour.

For example, the hex digit D corresponds to binary 1101. The 11 is ignored and the 01 is used to indicate colour 1.

Although the first two binary digits are always ignored, you may not assume they are always 00. They may take any value and all hex inputs of the correct length should produce a valid output.

### Coordinates

x and y are encoded as 2 hex digits each, most significant first.

For example, the hex string 2A corresponds to binary 00101010, and decimal 42

### Case sensitivity

Your code may accept input as either upper case or lower case hex digits, or both. If it only accepts one or the other case, it must also output in the same case.

You may not choose an arbitrary 16 characters to represent hexadecimal. You must use either (or both) of the following as input:

0123456789abcdef

0123456789ABCDEF


You must choose one or other (not both/mixed) to use as output. That is, you may accept inconsistent inputs if you wish to, but the output must be either always lower case or always upper case.

# Sandbox thoughts

• I'm considering adding example inputs and outputs and maybe a snippet to verify the output of arbitrary inputs for testing.

# Live Tennis Scoreboard

In this challenge, we're going to create a tennis scoreboard that could (theoretically) be used in an actual tennis match. The tennis scoreboard will display the score while listening on STDIN. As new results come in on STDIN, the tennis scoreboard will update itself accordingly.

### Description of Input

When the scoreboard is first instantiated, it will be provided input for two strings -- these are the names of the competitors. This can be via command line arguments, user input functions, etc.

After that, the scoreboard will recieve input via STDIN. These correspond to events that the scoreboard should reflect in the score.

• 0

The first player has scored a point.

• 1

The second player has scored a point.

• U

Undo the previous point and revert to the previous state of the scoreboard.

The scoreboard must handle games, deuces, etc. as described in the next section.

### Terse Description of Tennis Scoring System

This section here describes the exact rule set to use.

A match is between two players. To win a match, a player must win three sets. To win a set, a player must win at least six games and have a two-game lead over their opponent. To win a game, a player must win at least four points and have a two-point lead over their opponent.

The number of sets and games won are displayed as is. Points are displayed as follows in order of priority:

• 1 point = 15
• 2 points = 30
• 3 points = 40
• Number of points won are equal to the opponent = 40
• Number of points won are one greater than the opponent = Ad

Tiebreaks are optional. Implementing tiebreaks grants you -40 to your score.

### Scoreboard Format

During the first set and first game:

Name | x
Name | x


where x is the point display for each player.

During the first set:

Name a | x
Name a | x


where a is the number of games won by each player.

During the second set:

Name b a | x
Name b a | x


where b is the result of the first set.

During the third set:

Name c b a | x
Name c b a | x


where c is the result of the second set.

etc. for fourth and fifth sets.

Example:

Federer 5 6 6 3 2 | 0
Murray  7 4 4 6 2 | 15

• A bit of a far stretch, but it would be cool if you could point the programs at URL which gave the scores for an actual tennis match – Beta Decay Jul 27 '15 at 8:04

# Punch buggy?

As some of you might know, "punch buggy" is a children's(?) game that involves spotting Volkswagen Beetles and punishing other players. For reference, the car on the left is a punch buggy, while the car on the right is not:

Your task is: given an image, determine whether there is a punch buggy shown in it. Entries will be scored by percent correct among all n (TBD) test images. If there is a tie, it will be broken by run time on my computer (specs will be posted on main).

Test images may contain just about anything, and come in various sizes. Most will be automobiles of various types, but I will make sure they have a maximum of one auto in them (so if you see a non-matching car, you don't need to look for more). I won't use toy cars or heavily modified cars to try to fool you. Images will be pulled from Google Image Search, and will be of varying quality (from ad-quality to candid in-the-yard).

This is not a Kolmogorov complexity challenge. The point is not to recognize specific image files, but to recognize a Beetle in any picture. If it looks like someone is cheating this, I will change to a different test set and re-score.

### Spec

Input is the name of an image file in JPG or PNG format (should I restrict this to one?).

Output is Punch Buggy! if a punch buggy is present in the picture, and any other non-empty string if not.

Programs are run once per image. I will write a simple test controller for this using STDIO, so programs must be runnable from the command line, using a language that is freely available on Ubuntu.

You are allowed to read/write other files, but only in a folder with the relative path /yourProgramName. You are allowed to read files whose names are passed as input via STDIN.

### Sandbox

Yes, this seems a bit difficult to me, too. I don't see that as a problem. Is there anything that isn't clear about the task or spec? Other notes/questions/suggestions?

If it needs fluff (I'm not sure yet), it will probably be something like "help my robot become more human via children's games".

• Personally, I don't think this is that hard. You just look for a large grouping of yellow pixels around the centre of the image. I think you should limit it to a PNG. – Beta Decay Jul 29 '15 at 13:21
• @BetaDecay That would only work if all punch buggies are yellow and all other images/cars are not. The images shown here are only representative samples. The test cases will include various cars of various colors at various angles in various lighting conditions. – Geobits Jul 29 '15 at 13:27
• Ohh I thought Punch Buggy was when you have a yellow car, not just a Beetle – Beta Decay Jul 29 '15 at 13:30
• Ah. That's the Yellow Car Game. Similar, but yea, that would be a different difficulty level. – Geobits Jul 29 '15 at 13:32
• I afraid even if you people try to recognize buggies their results will come from randomness and overlearning on the provided images. Recognizing a car at all would be a difficult task itself. – randomra Jul 30 '15 at 11:49
• If you want to avoid this being a kolmorogov challenge, would it help to provide a much larger training set and test on a small subset of this that is not announced in advance? That does introduce a deadline excluding future submissions though. – trichoplax Aug 1 '15 at 18:30
• @trichoplax Not necessarily, because you could always test the new submissions using the subset (which is still unannounced) – Beta Decay Aug 5 '15 at 11:48
• @BetaDecay good point. That makes this sort of challenge seem much more promising. – trichoplax Aug 5 '15 at 12:27
• @trichoplax Though it could still be a kolmogorov complexity because a program could be programmed to recognise all pictures in the album, and choosing a subset wouldn't stop that program from getting full marks – Beta Decay Aug 5 '15 at 12:37

Question about symmetry in ascii grid (temp title)

Synopsis: Given a grid of ASCII characters, determine if, and in what ways, the grid is symmetrical.

Some characters are symmetrical to others. For example:

• d is symmetrical vertically to b
• W is symmetrical horizontally to M
• O is symmetrical both ways to O
• ! is symmetrical horizontally to i (takes some imagination!)
• ^ is symmetrical horizontally to v
• b is rotationally symmetrical 180 degrees to q (that is, if you rotate the first character 180 degrees, you get the second character)
• (space) is symmetrical vertically, horizontally, and rotationally to

In this challenge, there are only three types of symmetry that need to be considered: vertical, horizontal, and rotational by 180 degrees. You can find a full list of which characters are considered symmetrical at the bottom of this post.

If we arrange some characters into an n by m rectangle (where n and m are both even integers), then the rectangle may be symmetrical. Here is an example:

M^^^^MM^^M
OOOOOOOOOO
OOOOOOOOOO
WvvvvWWvvW


It is symmetrical horizontally.

Here's another example.

dddbbb
dddbbb
dddbbb
ddOObb


It is symmetrical vertically.

Here's one more example:

++++++
+p++q+
++++++
++++++
+b++d+
++++++


This one has three ways it is symmetrical -- horizontally, vertically, and rotationally.

Write a program which will, when given a rectangle of characters as input, output the number of ways that rectangle is symmetrical. For the three inputs I've shown above, the outputs would be 1, 1, and 3 respectively.

[Todo: list of characters]

## Sandbox Questions

1. One thing I've been considering is allowing entrants to access the list of which characters are symmetrical (in some sort of CSV format) in a file. This would mean that entrants wouldn't have to encode the symmetries themselves. On one hand, this probably saves some frustration at having to code in all the possible symmetries. On the other, this reduces the complexity of the challenge as the aspect of encoding the symmetries with minimal characters is removed. I'd like your thoughts on this.
• Yet more symmetries: all of []{}() are vertically symmetric to themselves. | belongs in "Both". lower-case c belongs in vertical. Maybe also lower-case a depending on the font your going by (apparently not the one used on SE). Likewise t might belong in horizontal symmetry. We also forgot about digits: 08 both ways, 3 vertical. – Martin Ender Sep 1 '14 at 11:58
• What do you think about adding rotational symmetry (by 180 degrees) to the mix? – Martin Ender Sep 1 '14 at 11:59
• ​​​​​​​​​​​​​Like 6 and 9? I think rotational symmetry would do well as a seperate question actually. – absinthe Sep 1 '14 at 12:08
• Yes, like 6 and 9. If a new question for that is based on the same concept, it would probably be too similar to not be a duplicate (at least the solution I have in mind would be rather easily adapted to do rotational symmetry, I think). Adding it here, might open some possibilities for interesting compression/golfing. – Martin Ender Sep 1 '14 at 12:11
• You've convinced me. I'll edit in the rotational part when I have time. – absinthe Sep 1 '14 at 12:14
• Since there will probably be combinations of all three symmetries on different characters, I'd recommend only having one list for each symmetry (with some pairs in multiple lists). Here are the rotational pairs I can think of: d/p, b/q, (/), [/], {/}, </>, %/%, ///, \/\, ,/,, S/S, s/s, z/z, Z/Z, W/M, !/i, ^/v, $/$, as well as all those which are symmetric both ways to themselves. – Martin Ender Sep 1 '14 at 12:22
• Some of the characters are not visible (at least on my screen) so would benefit from being followed by a description. I think they are just spaces but markdown appears to fail to display them even in backticks. – trichoplax Sep 1 '14 at 14:09
• Displaying a single space in an inline code tag has to be done with an actual <code> tag rather than with backticks. codegolf.stackexchange.com/questions/5194/… is a good starting point for rotational symmetries. Some digits also have linear symmetries. – Peter Taylor Sep 1 '14 at 14:39
• Would you also consider J and L as symmetrical (also requires a little imagination...)? – WallyWest Sep 2 '14 at 22:41