# Sandbox for Proposed Challenges

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

Sandbox FAQ

## Posting

Write your challenge just as you would when actually posting it, though you can optionally add a title at the top. You may also add some notes about specific things you would like to clarify before posting it. Other users will help you improve your challenge by rating and discussing it.

When you think your challenge is ready for the public, go ahead and post it, and replace the post here with a link to the challenge and delete the sandbox post.

## Discussion

The purpose of the sandbox is to give and receive feedback on posts. If you want to, feel free to give feedback to any posts you see here. Important things to comment about can include:

• Parts of the challenge you found unclear
• Problems that could make the challenge uninteresting or unfit for the site

You don't need any qualifications to review sandbox posts. The target audience of most of these challenges is code golfers like you, so anything you find unclear will probably be unclear to others.

If you think one of your posts requires more feedback, but it's been ignored, you can ask for feedback in The Nineteenth Byte. It's not only allowed, but highly recommended! Be patient and try not to nag people though, you might have to ask multiple times.

It is recommended to leave your posts in the sandbox for at least several days, and until it receives upvotes and any feedback has been addressed.

## Other

Search the sandbox / Browse your pending proposals

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## Add two real numbers ... probably

The problem statement here is pretty simple, take two real numbers between 0 and 1 as input and output their sum, with probability 1.

The catch here is that there are a lot of real numbers. There are in fact so many real numbers that it is impossible to fit all of them into any finite data type. As such any way to input real numbers has to be potentially infinite, and any algorithm that handles arbitrary real numbers cannot consume all of the input.

For this challenge you will input (and output) real numbers as lazy sequence (e.g. stream, generator, lazy list, function) of bits, representing their binary expansion. You can assume that the input will be normalized and will not end in an infinite repetition of 1.

Even with this special input format it isn't possible to add any two real numbers. Any potential algorithm can be tricked into an infinite loop.

So instead we are going to settle for almost working. To "work" on a pair of inputs your program needs to be able to output any bit of the input in finite time. For example, if you output a generator I should be able to read to the 5th bit without the program getting stuck in a loop. Your answer needs to work with probability 1, meaning that the measure of the set of inputs which your program does work needs to have measure 1. The behavior for which the program doesn't work is undefined it can loop forever give an incorrect answer etc. so long as these cases themselves have measure zero.

This is the goal is to minimize the size of your source code as measured in bytes.

• @AnttiP The number of inputs which require reading an infinite number of bits like this has measure zero. The solution here is to simply loop forever in the tough cases.
– Wheat Wizard Mod
Feb 9 at 12:42

# Posted here

• +1 just cause Dennis Feb 1 at 4:54
• Are the third and fourth test-cases correct? - I get different results. Maybe the 20 and 30 are swapped? Feb 9 at 14:40
• @pajonk right lol Feb 9 at 14:52
• Will all the steps result in integer apple numbers (step-by-step)? Currently it's not true for test cases 5 and 6. Feb 9 at 16:58
• @pajonk nope, ty Feb 9 at 19:21

# How many sorting networks?

Below on the left is a picture of a sorting network that can sort 4 inputs. On the right you can see it sorting the input 3,2,4,1.

A sorting network of size n consists of a set of n horizontal wires where two wires can be connected by a vertical wire. The inputs to a sorting network move from the left to the right on the horizontal wires and whenever a vertical wire connects two elements they swap places if the lower element comes before the higher element.

The example sorting network above has the property that it correctly sorts all inputs. You could add even more wires but the behavior would not change. But if you removed a wire then there would be some inputs that it would not sort anymore.

Two networks behave the same if for every input permutation they produce the same output permutation. Your task is to find out how many possible behaviors there are for a given size. That is, output a sequence of the number of behaviors (equivalence classes) for n=1,2,3,... etc.

Your code will be scored based on its speed on an AMD Ryzen 1800X linux system. The code should output the sequence described above and I'll run each submission for 5 minutes and with a 16GiB ram limit. Whichever code has outputted most of the sequence wins. Ties are broken by whichever program outputted the final number first.

Sequence output

1
2
11
261
43337
TODO


# Rotate an Image

• Might want to clarify if exif-orientations are allowed Feb 16 at 10:07

# Approximate a root of an odd degree polynomial

• I've got a couple of answers so vote for to move to main page :p Feb 18 at 19:32
• The only note: usually $a_i$ means coefficient of polinomial Feb 18 at 19:45

# Whole Number Groups

• Where does 1/7 come from in the second example? Feb 17 at 10:21

## Fibonacci Binary Squares

• since this is a sequence, can we just use the default sequence rules? Feb 21 at 1:01
• I'd be willing to allow the Fibonacci sequence used to generate the answer to be 0 or 1 indexed, but I don't see the logic in allowing the main "sequence" to be 0 indexed. The rest of the rules I think would be fine. Feb 21 at 11:55
• Well, some languages use zero-indexing for arrays, and some use one-indexing, so it can help. Feb 21 at 17:20
• Fair. Changed it to allow for 0- or 1- indexing. Feb 22 at 1:35

# "Candy Crush" a string

• Suggested test case: 1322232223222311 -> (1332223222311 -> 1333222311 -> 1222311 ->) 1311. Since you mention you reiterate after every replacement from left to right again (well done for making that bold). :) If one would filter out all blocks of 3+ at once, it would incorrect result in -> 1333311 -> 111 -> "". Good challenge overall, so +1 from me. And welcome to CGCC. Feb 21 at 12:19
• @KevinCruijssen Thank you for your feedback! I added your test case to the list :) Feb 21 at 12:43

# Help Me Type on My New Keyboard

• In the 5th test case first letter of output must be r not p Feb 20 at 20:36
• It is very hard to read q as я... can we remove this rule? :) I'm not expert but I have never seen that Russians use q as я Feb 20 at 20:41
• JFYI they widely use 4 as ч, so if you want you also can add this rule Feb 20 at 20:44
• @EzioMercer 1. Thanks. My english kicked in. for 2. and 3. this is the specific keyboard layout im using. most mnemonic layouts ive used use q as я Feb 20 at 20:48
• Your task your rules :) Also please remove additional space after second word in 5th test case Feb 20 at 20:51
• @EzioMercer read the comments after the test case: note the double space after "chtec". its required because c is a combining letter Feb 20 at 20:54
• And the last question :) Are you sure about these rules: "e" -> "е", "je" -> "э" and "ye" -> "э"? The letter j uses for я,ё,ю because in their pronunciation we have й at the start. я - йа, ё - йо, ю - йу and the same thing for letter е - йэ, so it is logical to have the these rules: "je" -> "е", "ye" -> "e" and "e" -> "э" Feb 20 at 21:02
• About c you already have the rule "c" -> "ц" you don't need any additional space after it Feb 20 at 21:03
• @EzioMercer yes im sure. i know it seems weird. for the second comment, note To type the single letters mapped to them, either press that key and then press space Feb 20 at 21:05
• You have weird keyboard :) Feb 20 at 21:06
• In 5th test case xepdyami -> xerdyami - change the p to r Feb 20 at 21:08
• @EzioMercer aargh the challenges of being bilingual :P Feb 20 at 21:10

# Largest Binary Area

• You may want to clarify that each column in ASCII art is a binary number. I had to read it a couple times before that was clear to me. Writing it out might probably be even clearer (e.g. "Take the sequence of all natural numbers in binary: [1,10,11,100,101,110,111,1000,1001,1010,1011,1100,1101,1110,1111,10000,10001,...]. Displaying each of these binary numbers as reversed columns gives: <insert current ascii-art here>") Apart from that the challenge is clear; nice challenge btw! I'm curious what kind of algorithms can be found instead of actually calculating the areas. Feb 28 at 12:51

# Calculate the p-adic square root of -1

Given a prime number $$\p\$$, a $$\p\$$-adic number is a number whose representation in base $$\p\$$ may have infinitely digits to the left of the radix point, but only finitely many digits to the right of it. A $$\p\$$-adic integer has no digits after the radix point.

$$\p\$$-adic numbers have some interesting properties. It can be proven that for any prime number $$\p\$$, there exists a $$\p\$$-adic integer $$\x\$$ such that $$\x^2 = -1\$$ if and only if the congruence $$\x_0^2 \equiv -1 \pmod{p}\$$ has a solution. (That is, there is some integer $$\x_0\$$ such that $$\x_0^2 + 1\$$ is divisible by $$\p\$$.)

Your task is to determine whether this is the case and calculate the digits of the number $$\x\$$. Note that there will always be two solutions which are additive inverses of each other; you only need to calculate one.

## Input

A prime number $$\p \ne 2\$$. (You don't need to verify that it's prime.)

## Output

Find the digits of the $$\p\$$-adic square root of $$\-1\$$, as described above. Following the standard sequence rules, do one of the following:

• Given an index $$\i\$$, output the $$\i\$$-th digit from the end. Since base representations are naturally 0-indexed, you may not use 1-indexing.
• Given a positive integer $$\n\$$, output the last $$\n\$$ digits. You can choose between little-endian and big-endian.
• Output all digits in the form of a non-halting program, a generator, an infitite lazy list, etc.

If the $$\p\$$-adic square root of $$\-1\$$ does not exist, do anything that can be clearly distinguished from a valid output, such as raising an exception or returning an empty list.

## Algorithm

Here I describe one possible way to solve this challenge.

• Find a number $$\x_0\$$ between $$\0\$$ and $$\p-1\$$ such that $$\x_0^2 \equiv -1 \pmod{p}\$$. If not found, report failure.
• Find a number $$\y\$$ between $$\0\$$ and $$\p-1\$$ such that $$\2x_0y \equiv 1 \pmod{p}\$$. (This is always possible.)
• Let $$\c_0 = \left\lfloor\frac{x_0}{p}\right\rfloor\$$.
• For each positive integer $$\i\$$:
• Let $$\h_i = c_{i-1} + \sum_{j=1}^{i-1} x_j x_{i-j}\$$.
• Let $$\x_i = (p-1-h_i)\cdot y \bmod p\$$.
• Let $$\c_i = \left\lfloor\frac{h_i + 2 x_0 x_i}{p}\right\rfloor\$$.
• The sequence $$\\left(x_i\right)\$$ is the output.

Ungolfed Python implementation:

def sqrt_minus_one(p, n):
for x in range(p):
if (x * x + 1) % p == 0:
last_digit = x
break
else:
return None # no solution
for x in range(p):
if (x * 2 * last_digit) % p == 1:
inv = x
digits = [last_digit]
carry = (last_digit * last_digit) // p
for i in range(1, n):
h = sum(digits[j] * digits[i - j] for j in range(1, i)) + carry
digits.append((p - 1 - h) * inv % p)
carry = (h + 2 * last_digit * digits[i]) // p
return digits


It's also possible to use a brute-force approach where you find an $$\n\$$-digit number $$\x\$$ such that $$\x^2 + 1\$$ ends with $$\n\$$ zeroes in base $$\p\$$. I suppose this could lead to much golfier solutions, so maybe I should make the challenge restricted-complexity to forbid this?

## Test cases

  p | first 20 digits (two possible outputs)
3 | ---
5 | 2,1,2,1,3,4,2,3,0,3,2,2,0,4,1,3,2,4,0,4
| 3,3,2,3,1,0,2,1,4,1,2,2,4,0,3,1,2,0,4,0
7 | ---
11 | ---
13 | 5,5,1,0,5,5,1,0,1,8,8,6,12,6,3,0,4,7,4,5
| 8,7,11,12,7,7,11,12,11,4,4,6,0,6,9,12,8,5,8,7
17 | 4,2,10,5,12,16,12,8,13,3,14,0,6,1,0,15,1,8,14,5
| 13,14,6,11,4,0,4,8,3,13,2,16,10,15,16,1,15,8,2,11
47 | ---
101 | 10,5,29,66,10,30,44,29,72,25,34,82,83,5,52,17,67,94,65,52
| 91,95,71,34,90,70,56,71,28,75,66,18,17,95,48,83,33,6,35,48

• Perhaps allow assuming a square root of -1 exists? Testing for the existence of it isn't too related to finding it 2 days ago

# Great Leap to the Right

Given a string s consisting of characters a-z lowercase, generate 5 arrays a1, a2, a3, a4, and a5 of size n (length of s) where the i-th element of each array represents the index of the next occurrence of the i-th character in s, with the following conditions:

• If no such occurrence exists, set the value to n (0-based indexing) or n+1 (1-based indexing) depending on the indexing convention you use.
• a1 represents the 1st next occurrence of the character, a2 represents the 2nd next occurrence, a3 represents the 4th next occurrence, a4 represents the 8th next occurrence, and a5 represents the 16th next occurrence.

This is a code golf challenge, so the shortest code in bytes wins.

Here are some test cases. They all use 0-based indexing.

Input: aakakakakka
Output:

1 3 4 5 6 7 8 10 9 11 11
3 5 6 7 8 10 9 11 11 11 11
7 10 9 11 11 11 11 11 11 11 11
11 11 11 11 11 11 11 11 11 11 11
11 11 11 11 11 11 11 11 11 11 11


Input: sydgdtsfixuvhdgisifdyovjcgs
Output:

6 20 4 14 13 27 16 18 15 27 27 22 27 19 25 17 26 27 27 27 27 27 27 27 27 27 27
16 27 13 25 19 27 26 27 17 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27
27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27
27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27
27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27 27


Input: qmorzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz
Output:

59 59 59 59 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59
59 59 59 59 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 59
59 59 59 59 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 59 59 59
59 59 59 59 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 59 59 59 59 59 59 59
59 59 59 59 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 59 59 59 59 59 59 59 59 59 59 59 59 59 59 59

• Having 5 arrays seems somewhat arbitrary. Perhaps have the number of arrays as an input? yesterday

# Is it a Frog List?

## Challenge:

A Frog List is defined by certain rules:

1. Each frog within a Frog List has an unique positive digit [1-9] as id (any 0 in a list is basically an empty spot, which can mostly be ignored).
2. A Frog List will always have exactly one Lazy Frog. A Lazy Frog will remain at its position.
3. Every other frog in a Frog List will jump at least once, and will always jump towards the right from its starting position.
4. When a frog jumps, the distance of its jump is always the same.
5. When a frog jumps, it will continue jumping until it's outside the list's right bound.
6. 0-1 jumping frogs can stand on top of a Lazy Frog, as long as their summed ids is still a single digit. (Jumping frogs cannot stand on top of one another! Which implicitly also means there cannot be two jumping frogs on a Lazy Frog simultaneously.)

Note that the frog-ids within a Frog List describe how a frog has already jumped (past sense). Focusing on an individual frog-id within a Frog List shows how it has jumped, and at what positions within the Frog List it has landed, and jumped onward from - with the exception of the Lazy Frog, which hasn't moved.

Worked out explanation of the first Frog List [1,2,1,0,8,2]:

1. The Lazy Frog has id $$\\color{green}{7}\$$ at position ~~~~7~:

1. The first jumping frog has id $$\\color{red}{1}\$$ at positions 1~1~1~ with jump distance 2:

1. The second jumping frog has id $$\\color{blue}{2}\$$ at positions ~2~~~2 with jump distance 4:

All three frogs summed gives the Frog List, so [1,2,1,0,8,2] would be truthy:

### All Test cases including explanation:

Input                 Explanation:


Truthy:

[1,2,1,0,8,2]         Lazy Frog 7 doesn't jump                ~~~~7~
frog 1 jumps (with jumping distance 2)  1~1~1~
frog 2 jumps (with jumping distance 4)  ~2~~~2

[1,0,0,0,0,1,2,7,2,2] Lazy Frog 5 doesn't jump                ~~~~~~~5~~
frog 1 jumps (with jumping distance 5)  1~~~~1~~~~
frog 2 jumps (with jumping distance 1)  ~~~~~~2222

[9,8,9,1]             Lazy Frog 7 doesn't jump                ~7~~
frog 1 jumps (with jumping distance 2)  ~1~1
frog 9 jumps (with jumping distance 2)  9~9~

[1,0,1,3,3,3,1]       Lazy Frog 2 doesn't jump                ~~~~2~~
frog 1 jumps (with jumping distance 2)  1~1~1~1
frog 3 jumps (with jumping distance 2)  ~~~3~3~
(Note that the 3 at ~~~~3~~ is Lazy Frog 2 and jumping frog 1 on top of one another,
and not jumping frog 3.)

[7]                   A single Lazy Frog 7

[7,0,0,0]             A single Lazy Frog 7~~~


Falsey:

[1,2,3,0,2,1,3]       (rule 2) there is no Lazy Frog: 1~~~~1~
~2~~2~~
~~3~~~3
TODO                  (rules 2 & 3) there are two Lazy Frogs (TODO: is this even possible without also applying to rule 6?)
[1,6,1,8,6,1]         (rule 4) frog 1 jumps irregular 1~1~~1 / 1~11~1
~6~~6~ / ~6~~6~
~~~8~~ / ~~~7~~
[2,8,2,8,0,9]         (rule 5) frog 2 stopped jumping 2~2~~~
~~~~~1
~8~8~8
[1,2,3,2,7]           (rule 6) two jumping frogs at the last position with: 1~~~1
~2~2~
~~3~3
(Lazy)~~~~4
^
OR two jumping frogs at the third and last positions with: 1~1~1
~2222
(Lazy)~~~~4
^ ^


## Challenge rules:

• The integers in the input-list are guaranteed to be $$\0\leq n\leq9\$$ (aka single digits).
• Any single-value inputs are Frog List, since they'll contain a single Lazy Frog and no jumping frogs.
• I/O is flexible. You may take the input as a list/array/stream of digits, an integer, a string, etc. You may output any two values or type of values (not necessarily distinct) to indicate truthy/falsey respectively.
• You can assume a Frog List will never starts with a 0 (doesn't matter too much for list I/O, but can be for integer I/O).

## General Rules:

• This is , so the shortest answer in bytes wins.
Don't let code-golf languages discourage you from posting answers with non-codegolfing languages. Try to come up with an as short as possible answer for 'any' programming language.
• Standard rules apply for your answer with default I/O rules, so you are allowed to use STDIN/STDOUT, functions/method with the proper parameters and return-type, full programs. Your call.
• Default Loopholes are forbidden.

# Sandbox questions:

1. Anything unclear?
2. Any missing rules?
3. Any suggested test cases?

# Sandbox TODO's:

• Reference implementation to verify larger test cases.
• Possible convert this to a challenge when the TODO above is done?
• It's definitely hard to make heads or tails of without referencing the test cases, but it's also hard to think of how to actually describe. Maybe start by moving the identification of frog ~= unique digit into the rules, and put something in about the number describing every position the frogs take throughout the described process? (I'm also not sure how simultaneity plays into it for the last falsy test case, under that interpretation, though...) Mar 15 at 10:19
• @UnrelatedString I've moved the first paragraph to the rules as requested. I've also moved the Test Cases section right below the Rules. (And replaced all x with ~, since I was looking for a suitable replacement character for it earlier.) After I've created a reference implementation with a larger test case, I might try to add a more in-depth step-by-step explanation of why it's a Frog Number perhaps. If you come up with anything to make the definition of a Frog Number clearer without having to look at the the example test cases, lmk. Mar 15 at 10:38
• Attempted an implementation. Though obviously faulty, it might be a usable starting point. Mar 15 at 11:02
• @UnrelatedString I've added some MS-Paint pictures of the first example and some more text explaining the Frog Number is the past sense of the jumping frogs (+ Lazy Frog). Lmk if this is somewhat clearer than just the rules + test cases. Mar 15 at 11:11
• Still unclear how the second true case works but the last false case doesn't, but the diagram is great! (Also, it does seem like the second false case should work as 9~9~ + ~1~1 + ~7~~--unless frogs' starting positions are constrained to be unique?) Mar 15 at 11:23
• @UnrelatedString Woops, you're complete right on both accords. The second truthy test case is indeed falsey because the last position contains two jumping frogs, and that is indeed a good find for the second falsey test case.. I really need to built a reference implementation before adding more test cases.. :/ Thanks for finding these errors! Mar 15 at 11:51
• I think 958 should work for two lazy frogs? The only way I can think of not having multiple lazy frogs requires multiple non-lazy frogs to occupy the same spot at once; yet at the same time there's at least four ways to do it with multiple lazy frogs. Mar 15 at 13:31
• @Bbrk24 You're right. 958 could also be a falsey because of rule 6 with just one Lazy Frog, as 1~~, 555; 3~3. I'm not sure whether it's possible to have a falsey test case that ONLY fails because of rules 2+3, since I think you can always find an alternative where it would fail for rule 6 instead with a single Lazy Frog. Either way it's falsey, so it's not too relevant tbch. I might just remove that TODO test case. Mar 15 at 13:38
• Why are these the digits of a number rather than just lists of positive integers? If there's no carrying it seems like the more convenient format for most solutions is going to be a list of integers, which makes the whole framing rather circuitous.
– Wheat Wizard Mod
2 days ago
• @WheatWizard Good point indeed. I've accepted lists as I/O in the rules, and mostly used integers because I wanted to restrict the frog-id to well.. digits, aka [1-9]. But I'll change it so a list of digits is the default I/O, and an integer is accepted as I/O as well. 2 days ago
• I think you should explicitly say "combined ids" means the sum of the ids, since addition isn't something you usually do with IDs 19 hours ago
• @CommandMaster Changed it to 'summed', and also made some other minor edits. 18 hours ago

# Huffman Decoding

Write a programm which takes two strings as input and prints a text.

The first argument is a Huffman Tree, serialized in the following format:

• every ascii character except ~ is always a leaf, if ~ is the first characater it is also a leaf.
• <tree0><tree1>~ is a tree where <tree0> is the left subtree and <tree1> is the right subtree.

Example: ab~cde~~~ generates this tree:

 ┌─┴─┐
┌┴┐ ┌┴─┐
a b c ┌┴┐
d e


where a would have the key 00, b 01, c 10, d 110 and e the key 111.

The second argument is a text that has been compressed with with the Huffman code that is defined by the first parameter. This bit-string can contain any bit sequence (also null-bytes and non-printable characters) and is not byte aligned, therefore it has been encoded with a variation of the standard Base64 encoding:

• the characters used for the encoding are the standard base64 characters: ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/
• the bitstring is broken up into 6-bit chunks and mapped to this characters
• if the last chunk is smaller than 6 bits, a character with this prefix is used, and padding characters are added to the string:
• - : the last chunk was five bits long
• = : the last chunk was four bits long
• =- : the last chunk was three bits long
• == : the last chunk was two bits long
• ==- : the last chunk was one bit long

Example:

bits:       1 1 1 1 0 1 1 0 1 0 0 1 1 1 0 1 0 1 0 0 0 1 1 0 1
chunks:    |1 1 1 1 0 1|1 0 1 0 0 1|1 1 0 1 0 1|0 0 0 1 1 0|1[0 0 0 0 0]|
characters:       9           p           1           G           g
base64:     9p1Gg==-


Your programm has to decode the text encoded in the second parameter and print it to stdout.

You have to provide your source code encoded in the way described above. The length of your encoded source code + the length of your serialized huffman tree will be the winning criterion.

TODO: example input

• It would be helpful to explicitly state the 64 characters used in the encoding. I presume they're A-Za-z0-9+/ but (especially if you're expecting people to implement that part explicitly) it's best to make the problem self-contained. Oct 8, 2012 at 16:23
• Hello! This looks like a good but abandoned meta post, would you be willing to offer it for adoption? (If you want to, you can still post to main.)
– user58826
Jun 9, 2017 at 15:30

## Polygon prefixes

Polygons are named after the number of sides that they have. A pentagon has 5 sides, an octagon has 8 sides. But how are they named? What's the name for a 248-sided polygon?

All polygons are suffixed with -gon. There are specific prefixes for each polygon depending on the number of sides. Here are the prefixes for the lower numbers:

3 - tri
4 - tetra
5 - penta
6 - hexa
7 - hepta
8 - octa
9 - nona
10 - deca
11 - undeca
12 - dodeca
13 - triskaideca
20 - icosa


Polygons with 21 to 99 sides have a different system. Take the prefix for the tens digit (found on the left column), the ones digit (right column below), and then stick a "kai" between them to get (tens)(ones)gon.

20 - icosi       | 1 - hena
30 - triaconta   | 2 - di
40 - tetraconta  | 3 - tri
50 - pentaconta  | 4 - tetra
60 - hexaconta   | 5 - penta
70 - heptaconta  | 6 - hexa
80 - octaconta   | 7 - hepta
90 - nonaconta   | 8 - octa
| 9 - nona


The 3-digit sided polygons are named in a similar fashion. A 100-sided polygon is called a hectogon. Take the hundreds digit, find it on the column for ones digits, then stick a "hecta" to its right. Now number off the tens and ones like above: (hundreds)hecta(tens)(ones)gon. If the hundreds place digit is a 1, don't put the prefix behind "hecta".

So, given an integer (3 <= n <= 999), return the name of an n-sided polygon. n-gon is not a valid answer :P

As with all code golf, shortest code wins.

Is the description good? Would it be harder if I instead asked for the number of sides, given a name?

• What is a 101-sided figure called? "hectahenagon"? Is "hena" from the column for ones digits you mention? If so, then what is a 111-sided figure called? I'd say "hectaundecagon", but then that comes from a column where "hena" is not present. Feb 11, 2013 at 11:15
• @Gaffi: Yep, it's hectahenagon, from what Google says. Feb 11, 2013 at 16:03
• I am going to take this if you allow me or if you don't respond
– user63187
May 30, 2017 at 1:13

## Code golfing problem: Surface classification

The task: Given a surface-word reply with the classification of what surface it is.

Example 1: Input: aba'b' ----> Output: 1T

Example 2: Input: aabcb'c' ----> Output: 3P

Bounds on the problem: Since there are only 26 letters, there will never be more than that many labels. Additionally output should be in the form S,nT,mP for n,m positive integers.

Background: In the study of algebraic topology students are often presented with diagrams such as the one below. The represent instructions for how to assemble a surface. The assembly is prescribed as: if there are two edges labeled with the letter x then glue them together so that the arrows point the same direction. To make our job easy, topologists have discovered an algorithmic way to classify surfaces using 'words' assembled from these 'plane gluing-diagrams'.

Choosing a corner arbitrarily (top right) and orientation (ccw) we read off the labels on the edges where an inverse appears wherever the arrow points against the orientation. In this case the 'word' that represents this plane model is given as abab.

A surface word is a string that contains the letters a,b,...,@ up to some letter @ and each letter is contained in it exactly twice. In the two occurrences of each letter: 0, 1, or 2 of them may be postfixed by a ' which I am considering using to represent 'inverse' (opposite orientation).

If in a surface word all letters appear twice: once without the ' and once with it (f.ex. ba'b'a) then we say that the surface the word represents is orientable. If a surface is orientable then it is necessarily the direct sum of n Tori for some non-negative integer n. If this condition doesn't hold (like in aab'b) then the surface represented is non-orientable: in this case it is the direct sum of m Projective Planes for some positive integer m.

Once you have found out if the reduced word is orientable or not, the final answer is given as follows. If orientable and number of unique letters in the reduced word is 1 then output should be S. Otherwise if the number of unique letters in an orientable word is n (it will be even) then the output should be sT where s = n/2. If the word is non-orientable then the output should be mP where m is the number of distinct letters in the reduced word.

The goal is to take as input some surface word, reduce it via reduction rules 1-6 and then classify it as a sphere, some number of connected tori, or some number of connected projective planes. Here are the 6 reduction rules where ~ represents 'reduces to':

Let M,A,B,C,D be surface words, x be a single letter, and juxtaposition represents concatenation:

1. Cycle Rule: If M = AB then M ~ BA
2. Flip Rule: M ~ M'
3. Sphere Rule: Axx'B ~ AB
4. Block Rule: ABC ~ ADC if B is a surface word and B ~ D by 1 or 2
5. Cylinder Rule: If M = AxBCx'D, then M ~ AxCBx'D
6. Möbius Rule: If M = AxBxC then M ~ AxxB'C ~ AB'xxC

I am looking for input on:

• should this be code-golf or programming-challenge?
• how would scoring work?
• ???

If I feel satisfied with the question in a few days I'll post it to the site.

• If, for each input, there is only one correct output, then it should probably be code-golf. The scoring criteria would then be source code length. Jun 8, 2013 at 14:33
• Yes, this is the case. In general however there is not a unique series of applications of the reduction rules for any given instance.
– Kaya
Jun 8, 2013 at 16:21
• I don't think the order of explanation is correct. You should explain reduction before talking about "the reduced word". And "reduce it via reduction rules" doesn't entirely make sense, because the rules are presented as equivalences rather than reductions, and most of them don't have a "natural" direction. Jun 10, 2013 at 8:49
• It's also occurred to me that you haven't defined the notation M'. Does it just consist of toggling the orientation of each token, or does it also reverse the entire string? And do you have test cases which between them force implementation of all of the reduction rules? Jun 11, 2013 at 8:32
• Good call on the string inverse, yes you have the right idea and I will make it clear. I have a lot of test cases from when I did a number of these computations by hand in a university course and (anecdotal experience) I am pretty sure that it is possible to force the use of all the reduction rules (except maybe 4 which is really just a meta-rule for convenience when doing proofs). Additionally you have alerted me to some concerns regarding the form of the proper output: it's definitely underspecified. I'll put some work into this today.
– Kaya
Jun 11, 2013 at 14:04

# Fastest Code: checking if interval pairs overlap

Given an unsorted input of many interval pairs (50+), write the fastest algorithm to determine if they do not overlap.

An interval pair is said to overlap if interval x and interval y are overlapping.

Example input 1:
interval x , interval y

10-25, 50-60
10-15, 25-60


Output:
Can be in any true false format.

false (They overlap)


reasoning:

a.x overlaps b.x
a.y overlaps b.y


Example input 2:

10-25, 50-60
20-30, 25-30


Output:

true (they do not overlap)


reasoning:

a.x overlaps b.x
a.y does not overlap b.y


Scoring:

[not sure...]
brute force gives a worst case n^2 runtime

• It's hard to understand what the program is supposed to do. It's better to give three separate self-contained test cases than to mix them together with extra identifiers which won't be in the actual input. But if I understand correctly, there's nothing difficult here at all. It's just interval overlap testing (two ifs) done twice for no obvious reason. Jul 5, 2013 at 19:45
• The problem is that there will be a very large input. I'm thinking > 50 lines. Jul 5, 2013 at 20:50
• I'm not sure whether or not to score it based on time, or worst case runtime. Jul 5, 2013 at 20:59
• Instead of asking for overlap, ask for disjoint: "Check if a family of intervals is disjoint". I also think it would be more interesting if you give intervals in interval notation but I you should at least specify whether or not the endpoints are included. Dec 21, 2013 at 7:41

I have no idea how to create a good code golf question!

See this description of a ray tracer with source code that fits on a business card. The author stopped when the code size was 1337 bytes.

Achieving identical output, optimise for minimum code size. Execution time is not relevant.

• I think what you have here is a straight ahead golf. All languages. You need only define the requirements. Do you want identical output or do you want "good output encompassing <list of features>"? Oct 6, 2013 at 17:22
• For a minimum feature list I'd suggest something like (1) it is ray tracer (2) supports point-like lights and shadow + ambient light (3) supports mirrored (implies reflection) and matte surfaces (3) all objects are sphere and overlaps are allowed. With no requirement for (a) anti-aliasing; (2) finite sized light sources; (c) atmosphere effect or (d) depth of field; or (e) tiling and gradients. Notice however, that the example supports at least (b), (d) and (e). Oct 6, 2013 at 17:29
• BTW--The one you linked can get a little bit more with #define Q return (R was already taken for the rand wrapper) and #define O operator. Oct 6, 2013 at 17:33
• I suggest reading the Teapot question in the sandbox Mk IV and the comments - it's not the same question, but some of the same issues are relevant, and it might give you ideas for improvements to the spec. Oct 6, 2013 at 22:48
• Yes. Read the teapot question for guidance. Ultimately I decided that one was too big, but we did get into some pertinent details. Dec 1, 2013 at 9:48
• This sandbox post has had little activity in a while and little positive reception from the community. Please improve / edit it or delete it to help us clean up the sandbox.
– user58826
Jun 9, 2017 at 15:32

# Countdown: Federal Holidays in the United States

Inspired by this question:

Christmas Countdown

Write a program or script that will countdown to the nearest U.S. federal holiday, at any given time, and will switch the display to an appropriate greeting during each holiday.

The following holidays must be tracked, and announced:

Holiday                         Date                    Greeting
==========================================================================================
New Year's Day                  Jan. 1                  Happy New Year!
Martin Luther King, Jr. Day     3rd Mon. in Jan.        Happy Martin Luther King, Jr. Day!
President's Day                 3rd Mon. in Feb.        Happy President's Day!
Memorial Day                    Last Mon. in May        Happy Memorial Day!
Independence Day                Jul. 4                  Happy Independence Day!
Labor Day                       First Mon. in Sept.     Happy Labor Day!
Columbus Day                    2nd Mon. in Oct.        Happy Columbus Day!
Veterans Day                    Nov. 11                 Happy Veterans Day!
Thanksgiving                    4th Thu. in Nov.        Happy Thanksgiving!
Christmas                       Dec. 25                 Merry Christmas!


The strings listed under "Holiday" and "Greeting" are all free. Shortcuts like "Merry X-mas!" or "Happy 4th of July" will count against you - the full and proper holiday names are free, so there's no good reason not to use them.

The following strings are also free, only when used as a label for time units or in advertising the next upcoming holiday:

days
hours
minutes
seconds
milliseconds
until
time


On any given non-holiday, the program must show a count-down timer which displays time remaining at least down to the second, and updates the display with an accurate value (according to the system clock) at least once per second. Time remaining until a holiday must be counted as the time until midnight (00:00:00) on that day.

How the days, hours, minutes, and seconds (and milliseconds, if you choose) are displayed is up to you, so long as all mandatory items are present and it is clear which numbers represent which value. Again, the strings defining units of time are free so there's no really good reason not to use them. (Though you won't be penalized for not using these strings, so long as it is still unambiguous which time units are which.) The program should also make apparent which holiday is being counted down towards.

On any given holiday, the program must cease displaying the countdown timer and instead display the appropriate greeting for that holiday from 00:00:00 until 23:59:59.

After a holiday is over, at 00:00:00 the next day, the holiday greeting must go away and be replaced with the countdown timer for the next holiday.

• Name of language
• Score (length of golfed code, minus free characters)
• Golfed code
• Total length of golfed code
• Total number of free characters used
• Un-golfed code, with descriptive comments

The program must be capable of running accurately (according to the system clock) at any time, and must be able to run indefinitely. The only limitations to this should be those imposed by the host computer or the nature of the programming language.

I'm considering changing some of the greetings, but I'm not quite sure what to.

• "Happy Martin Luther King, Jr. Day!" is just a mouthful and feels awkward, but shortening it to "Happy MLK Day" feels weird too - any other suggestions?
• I'm not quite sure "Memorial Day" should really be preceded by "Happy" - thoughts?
• Any others?
• I think it would be more interesting if the strings were not free, but you still required exact match. I would like to see the compression scheme used by contestants. Dec 7, 2013 at 12:04
• @JanDvorak This is meant to be code-golf, not kolmogorov-complexity.
– Iszi
Dec 7, 2013 at 22:11
• This challenge proposal has been inactive for over a month. I would like to take ownership of the challenge and make it ready for posting. Please let me know within the next 14 days if you have any objections and would still like to finish and post this challenge yourself.
– user10766
Nov 3, 2014 at 2:01

## Golf a random Human Genome fragment with non-random features

A totally random genome fragment is easy enough: just spit out the letters ATCG in random order, and you're done. So let's try something a little less random and more useful to science.

• Accept an argument from the user for number of base pairs (20bp-10000bp must be supported, more if you wish)

• Accept an argument from the user for GC content. This indicates how frequently the generated sequence should contain the G and C bases as a percentage of total sequence length.

• Include at least one complete gene in every request of 500bp or more, where a gene is defined as an otherwise random sequence that begins with a start codon triplet (ATG) and ends with the first stop codon triplet it encounters (TAG, TGA, or TAA). The distance between the start codon and the stop codon does not have to be a multiple of 3.

• Vary gene content (the portion of the fragment that is "gene", inclusive of the gene's start and stop codons) linearly with respect to GC content (when sequence >= 500bp). At the extremes, when GC content is 0%, gene content is 10%; when GC content is 100%, gene content is 60%.

• Output a single-strand sequence that complies with the above specs and the user's given parameters. (i.e. a single row of letters will suffice since it is trivial to deduce the complementary strand of the DNA given the sequence of one strand)

• Calculate the actual GC content %, actual number of genes, and actual gene content % in the resulting fragment, and output a status line below the sequence conforming to the example format below. Percentages may be rounded to one decimal place. Actual values may deviate by +/- 3% from the expected outcome based on user's input.

GC content: 42.1% | Genes: 3 | Gene content: 32.1%

• Use any Internet, library, or built-in gene sequence generation functions or databases. Roll your own.

Sufficient randomness:

• For the purposes of this challenge, any built-in random/pseudo-random number generator function, GUID generator, well-seeded cryptographic hash function, etc. is considered an acceptable source of randomness.

What-ifs:

• What if another start codon occurs before the stop codon? E.g. ATGXXXATGXXXXXXXXXXXXTAG. This is acceptable, but the "gene" length in this case is calculated from the most proximal start codon to the stop codon.
• What if another stop codon occurs after a stop codon? E.g. ATGXXXXXXXXXXXXXTAGXXXXXXTAG This is also acceptable, but likewise the "gene" length is calculated from the start to the most proximal stop.
• What if both of these things happen? E.g. ATGXXXATGXXXXXXXXXXXXTAGXXXTGA. Here again, the "most proximal" principle applies and the gene content is demarcated by the innermost start and the innermost stop.
• Do "orphaned" start and stop codons that do not demarcate a gene count as gene content? No.

This challenge is code golf, so shortest valid code wins.

Post example output from a 500-bp request with GC content between 35% and 65%, and have fun!

• "Use hardcoded fragments for anything other than the start and stop codons." - why not? Specifying criteria for what counts as enough randomness should make these useless in any case. Speaking of which, you need to specify criteria for what counts as enough randomness. Feb 28, 2014 at 5:54
• The only partial output example given flagrantly violates the spec. If the GC content is 42.1%, the gene content should be 31.05%, not 22.0%. The definition of "gene" is also imprecise: in the sequence AUGCCAUGCCUAGCUAA, which is the gene? Feb 28, 2014 at 12:02
• @PeterTaylor AUG starts the gene, then come the CCA, UGC, CUA and GCU triplets, none of which terminate the gene. Now if there were three C's instead of two, then UAA would be the terminating triplet and the whole sequence would form a gene. I agree the definition is imprecise, though. Feb 28, 2014 at 12:11
• @JanDvorak, (part of) the point of that example is that there are two AUG substrings. Feb 28, 2014 at 12:30
• Good points. I was hoping to avoid having too much text, but that came at the expense of less clarity than the challenge demands. Edit forthcoming. Feb 28, 2014 at 13:58
• Also, I've muddied the waters with RNA encoding and DNA encoding, (U vs T), which we can chalk up to a late night. Feb 28, 2014 at 14:00
• Revised accordingly, although I remain open to suggestions on how best to frame the standards for acceptable randomness. I want something that won't be exploited by answers making no effort at randomness, but that doesn't have the pain-in-the-butt factor of generating 10mb+ of data and running a Diehard test battery. Feb 28, 2014 at 17:20
• " This is acceptable, but the "gene" length in this case is calculated from the most proximal start codon to the stop codon. " - wait, what? In nature, the first one is the start codon, and the rest encode methionine. Under your scheme, methionine (which is an essential amino-acid) would be impossible to include into proteins. Your scheme would also be much harder to splice. Also, what happens to AUG substrings that are not triplet-aligned to previous AUG substrings? Mar 1, 2014 at 9:25
• In nature, the first ATG encodes the start of a protein coding region and defines a reading frame (triplet boundary), the rest encode methionine and the first triplet aligned stop codon encodes the end of the protein coding region (and no amino-acid). Mar 1, 2014 at 9:29
• As for the randomness, I'm not worried about the source of randomness (whatever native library is available is assumed to be good enough) but rather how the source of randomness is used (can we just start the sequence with a start codon and insert an end codon at just the right spot if it doesn't occur naturally sooner, then fill in with more random codons while avoiding ATG subsequences? Your "sufficient randomness" places constraints on the RNG (useless) but no constraints on how it's used (or that it needs to be used at all) Mar 1, 2014 at 9:34
• My true random number sequence generator was sitting there watching silently as I typed away the sequence ACACACACACACAC.... It's all okay. The TRNG was capable of producing something better - it just didn't really get to it. Mar 1, 2014 at 9:38
• In fact, the 3% tolerance for the CG content leaves no room for randomness when there are only 20 base pairs. I can shuffle the pairs and turn some A<->T or C<->G, but that's it. In fact, if the CG content is set to zero, the task is impossible: we want a gene content of 2 base pairs (which is itself impossible), but the start codon contains a G, and a single G in a 2bp sequence means a 5% CG content, 2% than is the limit. Not including a gene means that we are 7% under the gene content lower limit. Similarly, it's not possible to start or stop a gene with nothing but Cs and Gs. Mar 1, 2014 at 9:45
• Yeah, the 20bp starting point is a bad idea. The problem with start codons is that I considered introducing the idea of promoters and decided that would make the whole thing too complex. So in the absence of promoters there has to be some way to determine which Met is the start codon vs an amino acid and the easiest simplification is to have no Mets in the gene. Likewise, for "not triplet aligned", I'm trying to avoid having to go into explanations of frameshift mutations (even though a Frameshift% would be a cool parameter). Mar 1, 2014 at 14:29
• I am starting to think that all of these complexities should be included (this proposal stems from me noticing that most of the extant random DNA generators are pretty weak) and this should just be a popularity contest instead of a golf. Link a couple of good articles on the structure of the genetic code and let people add as many features as they wish. Making it a golf seems to be a catch-22 between too many compromises or a too-impenetrable wall of rules and conditions that will dissuade participation. Mar 1, 2014 at 14:33
• Perhaps a code-challenge where people earn x points for each complexity implemented?
– user10766
Mar 2, 2014 at 5:52

## DIM, the DIM Integer Machine

The DIM Integer Machine is an engine for producing integer sequences.

It has one major problem: To put it mildly, it's kind of...dim.

After producing a single number, it immediately forgets what sequence it was working on. The only thing it remembers is the last number it produced and the current direction of the search, either ascending or descending. (And of course, it remembers the methodology for finding numbers according to the commands it understands).

Consequently, the user is free to change their mind after each number by issuing a new command.

Suppose the DIM has just produced an integer square: 81

• User inputs P and submits the input.
• DIM understands that P is requesting the next prime number after 81
• DIM computes and returns 83.
• DIM forgets what it was doing.
• User inputs O.
• DIM understands that O is requesting the next odious number and returns 84.
• DIM forgets what it was doing.

The DIM functions only for numbers between 1 and 1,000,000. If the DIM reaches either extreme while performing a search it will reverse direction and continue searching.

(For example: If searching in ascending order for a prime when the last number was 999,999, it will encounter 1,000,000 which is not a prime, then switch to descending order and continue searching for the "next" prime by moving downward - 999,999...999,998, etc.)

The DIM remembers the last number as 1 when it is first activated for a searching session.

This is the full list of commands that the DIM understands:

• P - Next prime number
• S - Next square number
• F - Next Fibonacci number
• O - Next odious number
• W - Next wasteful number
• U - Next undulating number
• K - Next katadrome
• R - Reverse direction immediately; the next command will proceed in the new direction

Because the DIM is so...dim, it absolutely DOES NOT precompute lookup tables of numbers in these sequences. It is far too forgetful for that to work. The DIM also has no Internet connection, so it is unable to consult the Online Encyclopedia of Integer Sequences or other such sites. It also has a sense of pride, so it does not make use of built-in Fibonacci functions or NextPrime / PrimeIndex / PrimeTest type functions.

Given the parameters it knows - a starting number, a search direction, the type of number to find - it simply computes the next number by some means other than mere data retrieval.

The DIM may accept input interactively, or from a newline-terminated text file, or from a pre-initialized array. You may not pack extraneous data other than the command sequence into the input - play fair!

This is a code golf, so least number of bytes wins. Submit your program with output results for the following search sessions:

1. P O U R F O R U S O U R P R O W S
2. W O R K F O R P O O R F O R K S K O O P S R O O K S F O U R W O W S
3. P O O P O O P O O P P O O P P R O P S P R O W S P O R K S

It is assumed that you know what prime, square, and Fibonacci numbers are. A brief explanation of the other integer sequences follows.

Odious - a nonnegative number which has an odd number of 1s in its binary expansion. The first few odious numbers are 1, 2, 4, 7, 8, 11, 13, 14, 16, 19

Wasteful - a natural number that has fewer digits than the number of digits in its prime factorization (including the exponents). The first few are 4, 6, 8, 9, 12, 18, 20, 22

Undulating - has alternating digits of the form aba, abab, ababa, etc. Assume all U numbers are non-trivial, i.e. 3 digits or more. The first few: 101, 121, 131, 141, 151, 161, 171, 181, 191, 202, 212

Katadrome - A number whose hexadecimal digits are in strict descending order. The first few are 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 32, 33, 48, 49

• When I post the question, I'll also include external links to MathWorld or OEIS for those who need more detail on the less familiar sequences, but the explanations above should be sufficient for most, I think. Mar 6, 2014 at 23:28
• Your definition of "undulating" isn't the one I'm familiar with, which just requires that the digits alternately increase and decrease. Also, it would be better to include expected answers for the test cases, so that submitters can use them as test cases rather than them serving just for you to say "No, this is buggy". Mar 6, 2014 at 23:57
• Yes, that's my plan, I just haven't finished double checking my results for the test cases yet. OEIS and Mathworld have the strict 2-digit definition of undulating, but I'll make sure to make the definition here more prominent so it is clear which interpretation is meant. Mar 7, 2014 at 0:04
• Hello! This looks like a good but abandoned meta post, would you be willing to offer it for adoption? (If you want to, you can still post to main.)
– user58826
Jun 9, 2017 at 16:09

# Unified format patcher

Write the shortest program that will take a patch file in the unified format from stdin and apply that patch. No external tools that do the process for you can be used.

### Clarifications

• Extra documentation about the unified format can be found here
• All file paths will be relative
• Only one file will be modified per patch
• Timestamps can be ignored
• The patch file will be valid and will apply cleanly to the file specified (it will not lie about line numbers, etc..)
• Assume all files being patched already exist, you don't need to create/delete files

### Extra

• -35 - Take an argument that allows you to unpatch a patch

### Example

/test/a.cpp

#include <iostream>
using namespace std;

int main() {
cout << "Hello world!";
return 0;
}


patch.txt

--- a/test/a.cpp
+++ b/test/a.cpp
@@ -1,7 +1,8 @@
#include <iostream>
+#include <vector>
using namespace std;

int main() {
-    cout << "Hello world!";
+    cout << "Goodbye world!";
return 0;
}


Run patch

patch.exe patch.txt


/test/a.cpp

#include <iostream>
#include <vector>
using namespace std;

int main() {
cout << "Goodbye world!";
return 0;
}

• Can the program assume that the @@ lines contain the correct line numbers? Mar 6, 2014 at 17:52
• A good explanation of the patch file format is needed. If not too long, include it in the question. Else, provide a link. Mar 6, 2014 at 17:53
• You forgot the obvious "no external tools" disclaimer. You don't want the patch \$1 answer. Mar 6, 2014 at 17:55
• @ugoren thanks for the comments, I added some further clarifications. Mar 6, 2014 at 18:38
• Does "The patch file will be valid (it will not lie about line numbers)" also mean that it will apply cleanly? Mar 6, 2014 at 19:24
• @PeterTaylor yes, updated question. Mar 6, 2014 at 19:51
• "The shorted program" should say "the shortest program", but other than that I think it's ready to go. Of course, no-one's actually going to do more than filter out the lines starting -, remove the first char from each line, and parse the line-numbers to work out how to splice the resulting text in. Mar 7, 2014 at 0:01
• This sandbox post has had little activity in a while. Please improve / edit it or delete it to help us clean up the sandbox. Due to community guidelines, if you don't respond to this comment in 7 days I have permission to vote to delete this.
– user58826
Jun 9, 2017 at 16:10

# Efficient Testing for Armstrong Numbers

An Armstrong Number (also known by different names, including Narcissistic Number; see Wikipedia for more information) is a non-negative number (for our purposes represented in base 10) that is equal to the sum of the individual digits of the number each raised to the power of the number of digits. For example:

2. The individual digits are 4, 0, & 7.
3. Since it is a three digit number, we raise each digit to the third power: 64 (4^3), 0 (0^3), & 343 (7^3).
4. The sum of those values is 407 (64 + 0 + 343).
5. Because the final sum is equal to the original number, it is an Armstrong Number.

By contrast:

2. The individual digits are 4 & 7.
3. A two digit number, so raise each digit to the second power: 16 (4^2) & 49 (7^2).
4. The sum of those values is 65 (16 + 49).
5. The final sum of 65 is not the original number, so it is not an Armstrong Number.

Your mission, should you decide to accept it: Write a program in any programming language (using only standard language features and libraries) implementing the most efficient algorithm possible to test the numbers from 1 through 18,446,744,073,709,551,615 (264-1) inclusive for "Armstrongness", generating a list of Armstrong Numbers, and only Armstrong Numbers, as output.

While any language is acceptable, it should be obvious that interpreted scripting languages will be at a disadvantage in the efficiency department. That being said, a superior algorithm in an interpreted scripting language can beat the pants off an inefficient algorithm in hand tuned assembly language.

## Winning Criteria

The algorithm that can check all possible candidate numbers for "Armstrongness" in the least amount of time on a reference computer will be the winner. The reference computer will have the following specifications: {approximately an AMD Phenom class computer with 8 GB RAM running Windows 7 Ultimate 64 bit}

• I don't know that this would belong in the (already very long, maybe too long) problem statement above, but other historical background. The class was for Fortran 77, and I was in a friendly competition with my TA to write the shortest version. I never could win that one, so I decided to write the most efficient version instead. Hence: I prefer efficiency puzzles to code golf (though code golf is fun too). Feb 20, 2014 at 8:30
• This doesn't seem to have an objective winning criterion. You do list "criteria I'll be using to judge this", but a) it mixes specification with winning criteria; b) it combines factors without indicating their weight. Feb 20, 2014 at 11:51
• The question also seems to be about twice as long as it needs to be. If you use the [link text](url) link notation you can shorten it slightly; you can also lose paragraphs by cutting the worked example and brute-force code (link to the existing question on narcissistic numbers instead); cutting the waffling about which languages you think have advantages; and simplifying the motivation. Feb 20, 2014 at 11:57
• I think efficiency problems are not well suited to code-golf. The efficiency of an algorithm depends on too many factors. You could perhaps require the lowest number of power operations. Feb 20, 2014 at 12:43
• @ugoren, 0 is easily obtained. Feb 20, 2014 at 12:57
• @PeterTaylor, You're right. Still, trying to replace a time measurement with the number of operations of a certain type sometimes helps define the problem better. Feb 20, 2014 at 15:12
• @PeterTaylor: I agree it is quite long, and will consider revisions to it. Feb 20, 2014 at 21:43
• @PeterTaylor: I'm open to better phrasing of the "objective winning criteria" but really, it is pretty objective already. One, no wrong answers allowed in the winner. Two, how efficient is the algorithm (based on the range of numbers tested and time taken to test them). For example, an algorithm that tests all numbers through 9 digits in 100 seconds is faster than an algorithm that takes 20 seconds to test all numbers through 8 digits (10 times larger interval in only 5 times the time). How might you suggest integration of this with the problem statement? Feb 20, 2014 at 21:48
• @PeterTaylor: Glad I included the disclaimer about failing eyesight, given that I searched for narcissistic numbers and came up with nothing. I either searched the wrong portion of PCG (meta) or I made a typo when spelling narcissistic. Feb 20, 2014 at 21:49
• @ugoren: efficiency may not be suited to code golf, but my understanding was that this 'forum' was about "programming puzzles" and "code golf". I certainly would consider finding a more efficient algorithm to be like solving a puzzle, though maybe I'm alone in that, in which case no biggie. Feb 20, 2014 at 21:51
• Edited the problem statement (which is still admittedly quite long, still considering other edits) by removing the final PPS paragraph and replacing the existing links as suggested. Feb 20, 2014 at 21:59
• The winning criterion is still too imprecise IMO. (NB Of the judging criteria you list, the first is part of the spec, so it's an acceptability criterion rather than a winning criterion). A genuinely objective winning criterion allows me to calculate my score before I submit my answer. Mar 12, 2014 at 8:47
• It should be much shorter in order to not discourage people from approaching your challenge. Almost all the text after the definition doesn't add anything to the challenge - beside "don't print wrong numbers" which is of course relevant. I also think that a more precise criterion should be given instead. Mar 12, 2014 at 9:03
• I've posted a "radical" update to it. I suspect the new winning criteria will not be acceptable either, since it involves a "reference computer" for final timing. Very open to suggestions on how to restate it so that a crappy algorithm on fast hardware doesn't beat an efficient algorithm on slow hardware. Mar 12, 2014 at 20:17
• The possibility that processor architecture or available memory affects the results is a tricky issue with fastest-code questions, but there isn't really a better way of comparing speed of programs than measuring on a large test case. I can at least measure how my program compares to someone else's on my computer, and know whether it's close or not. Mar 12, 2014 at 21:23

## Amino Acids Matcher

In genetics, a codon is a set of three nucleotides, the most basic form of nucleic acids. A codon "codes" (no pun intended, that's the actual term used) for a specific amino acid. Given a string of DNA, it is converted into RNA form by taking the opposite complementary pair.

DNA    RNA
A      U (T changes to U)
T      A
C      G
G      C


You will be given a String of unknown length that contains multiple codons. You must convert them to RNA form and print out the amino acid for each. See here for a chart: http://en.wikipedia.org/wiki/RNA_codon_table#RNA_codon_table

## Sample Input

TACTCGGATACT

Is split into

TAC, TCG, GAT, ACT

We now change each letter to its reciprocal

AUG, AGC, CUA, UGA

And print out the amino acids

Methionine, Serine, Leucine, Stop

This would probably be

I know that this is most likely not sufficiently explained and might be too complicated. Additional, tell me if there is any incorrect information above.

• So basically this is a challenge to compress a lookup table. You should probably specify that the string will be a multiple of three characters (or specify what to do otherwise); and it would seem sensible to inline the lookup table so that a) the question doesn't rely on the external page remaining intact; b) you save everyone who wants to answer the question the hassle of calculating it. Mar 17, 2014 at 12:42
• Thanks for the feedback. I'll update accordingly later today. Mar 17, 2014 at 15:48

# Find words in word square solver

On social media I often see images with letters and in them are some positive words for people to find. I challenge you to write a program that finds all words in the puzzle that matches a input dictionary. An example of such puzzle is this one:

An ASCII representation I made of this:

XCUALOVEYKBWSNG
DUAWKCBEAUTYRJV
YOUTHFSMGNEZLPR
MHJREYWDKZLUSTJ
FSUCCESSDHEALTH
ENMQXPTIMELMSAQ
VEXPERIENCEGHBW
GHUMOURLOYMONEY
SYZPOPULARITYNA
AMKCFUNBXHUZYIX
CWIHYSHAPPINESS
HONESTYCFRIENDS
KPYJAETWPOWERQC
BTYACFREEDOMJMO
RIWINTELLIGENCE


Now I imagine we can find words horizontally, vertical and diagonal and all of the mentioned in reverse. The program must be able to take a square and a dictionary like this one and print all the matching words.

As a test case I give custom dictionary:

bar
bid
dir
dog
fed
foo
god
man
mod
set
sun


And a test square:

OGFIR
DOMAN
ODBID
OPGES
OGFIR


Your code should be able to print all but the two last words in the dictionary. For diversity you should specify how the cube and the dictionary is bo be entered.

This is so shortest code wins.

• What should be output? Only the matched words? Their positions? And directions? Apr 3, 2014 at 15:47
• @JanDvorak Just print the words found. Do you think coordinates and direction can be given a bonus? Apr 3, 2014 at 15:51
• Cube? I'm only seeing two dimensions. On a more general note, perhaps for questions of this sort it would be OK to assume the availability of a standard dictionary file like /usr/share/dict, and discount the characters used to access this file? What do people think? Apr 3, 2014 at 15:55
• @squeamishossifrage OMG You're right. I meant square of course :-) I think people can choose. eg. The question is open for diversity like cat square.txt dic.txt | solver now, but I'm open for change that does not discriminate. Apr 3, 2014 at 16:03
• How does the program know where the wordsearch ends and the dictionary starts? Apr 3, 2014 at 21:39
• @PeterTaylor By mistake I made the test a rectagle, but I fixed that. The length of the first line would be the number of lines in the square. Anyway how the input is done I thought should be up to the solver so that they can choose to open files, read stdin or maybe more disturebing ways to get input in... Apr 3, 2014 at 21:47
• Hello! This looks like a good but abandoned meta post, would you be willing to offer it for adoption? (If you want to, you can still post to main.) Due to community guidelines, if you don't respond to this comment in 7 days I have permission to adopt this.
– user58826
Jun 9, 2017 at 16:30
• @programmer5000 It only got two upvotes so I let it be. Feel free to post it if you'd like. Jun 12, 2017 at 15:27

## Collatz ...something

The Collatz conjecture states that every natural number n leads to the number 1 if the recursive function f(n) is applied to it defined as

f(n)=n/2    if n is even
=3n+1   if n is odd


Let "ai" be the value of f applied to n recursively i times so that a0 = n , a1 = f(n) , a2 = f(f(n)) ... ai = f(ai-1)

Let A be the set {a0, a1, ..., 1}

Thus, for n=10, we get the sequence

a0 = 10 --> a1 = 5 --> a2 = 16 --> a3 = 8 --> a4 = 4 --> a5 = 2 --> a6 = 1

and the set A as A = {10,5,16,8,4,2,1}

Your task is to write a function/program that will accept a set of naturals say I. You must output a set of numbers say C such that I is a subset of the union of the sets A for all numbers in C.

### Rules

• Network access is forbidden
• Any of the standard loopholes are forbidden
• Your program must end in less than 200 seconds. You may assume that all the input terms are less than 2^(45); however note that the individual terms of the collatz sequence can go higher.

### Input

• List/array of naturals in I as an argument to a function
• , or space or \n separated naturals in I on STDIN

### Output

• return a list/array/set of all naturals in C
• print all the naturals in C separated by \n

### Scoring

( ( (10)^(number of elements in C) ) * (sum of all elements in C) ) + ceil( 100*log(total number of bytes of your code) )


log() is the natural logarithm

Lowest score wins.

### Examples

Input:

I = { 16 , 32 , 40 }


Possible outputs along with the score

C=                   Score

{ 16 , 32 , 40 }     ((10)^(3))*(16 + 32 + 40) = 8000   + constant
{ 32 , 40 }          ((10)^(2))*(32 + 40)      = 7200   + constant
{ 32 , 13 }          ((10)^(2))*(32 + 13)      = 4500   + constant --> most optimal
{ 1024 , 320 }       ((10)^(2))*(1024 + 320)   = 134400 + constant
... Infinitely many higher numbers


where constant is ceil(100*log(code length))

In this case, the answer { 32 , 13 } is the most optimal.

Note: This is NOT code-golf even though the length of your program is considered. Please also provide a readable version.

I'm being flexible with the I/O so that the more verbose languages might get some benefit. You can write a complete program or a function or a lambda function. It is not required that your function(if you choose to write one) returns. Using a function for input while printing the output is fine if that makes the code shorter.

This will be tagged as

## Sandbox feedback

• Can anyone suggest a better title?

## TODO

• Scoring needs specific test cases. Perhaps the final score could be the average of all scores of the test cases.

• Needs a proper title.

• The timing constraint is not reasonable unless you also provide constraints on the number and size of the inputs. For any input for which the constraint is reasonable at all, I think that the first point of the spec is unnecessary: if a counterexample exists, it's right at the edge of what fits in a 64-bit number. The second point of the spec is currently quite difficult to understand. Apr 3, 2014 at 9:47
• @PeterTaylor Is it OK now? Apr 4, 2014 at 16:15
• Looking around a bit at the standard terminology, I think that it might be best introduced with something like "Each positive integer n generates a Collatz sequence by repetition of the map f(n) = n % 2 == 0 ? n/2 : 3*n+1. Define the orbit of n as the set containing the integers in its Collatz sequence, and the orbit of a set {n_i} as the union of the individual elements' orbits. Your task is to find an optimal set under the constraint that its orbit contain a specified subset." That then leads into the example. Apr 4, 2014 at 16:48
• I'm not sure that it's justifiable to claim that for your example {I2, C5, C10} is "(not the most ideal)". Whether or not it is depends on which arrows are /2 and which are *3+1, which isn't shown in the example. It's also occurred to me, which I missed earlier, that your scoring system requires a bit more of a test suite: at present, you have no way of distinguishing between answers which get the optimal solution to one test case. And I suggest a title, based on my previous comment: "Optimal Collatz orbits". Apr 4, 2014 at 16:52
• I suggest you to add a link describing what is a collatz sequence. As a non-mathematician, I find it hard to understand. There is extra whitespaces after  in your first code block.
– A.L
Apr 4, 2014 at 17:12
• @PeterTaylor Edited a lot. Are you sure it is called an orbit? I couldn't find that term anywhere. Apr 6, 2014 at 16:39
• It occurs 4 times in the Wikipedia page on the Collatz conjecture, and Google gives over 6 million hits for collatz orbit. Apr 6, 2014 at 22:08
• Hello! This looks like a good but abandoned meta post, would you be willing to offer it for adoption? (If you want to, you can still post to main.) Due to community guidelines, if you don't respond to this comment in 7 days I have permission to adopt this.
– user58826
Jun 9, 2017 at 16:31

# Filter out repetitive lines

Google Suggest doesn't show any results if a string contains more than 4 repetitions of a substring. More specifically, if a substring is repeated 4 times in a row, followed by the first character of that substring (i.e. abcabcabcabca or x x x x x), nothing is suggested. This rule changes slightly if the substring is all the same digit - a digit may be repeated 5 times in a row, but no more. This is probably to allow searching for ZIP codes like 22222. (This doesn't extend to strings like 1010101010, though.)

Let's simulate this behavior! Write a program that takes lines on standard input and echoes those lines back on standard output, unless the line fits the criteria for repetitiveness, in which case it's silently discarded.

Sample input:

a simple query
nananananananana
ffffgggghhhh
48719999936
abc abc abc abc asdf
xyzzzzzyx
122333444455555666666
repetitiverepetitiverepetitiverepetitive
erepetitiverepetitiverepetitiverepetitive
101010101
55555 zzzzz


Output:

a simple query
ffffgggghhhh
48719999936
repetitiverepetitiverepetitiverepetitive


(Google's behavior is actually quite a bit more complicated than this; there are a few exceptions to all of these rules, but let's just ignore those for this challenge.)

There was a similar challenge posted awhile ago (Recognizing Repetition in strings), but it was closed due to vagueness. I think the criteria proposed above are more than thorough enough.

• The current exceptions make it complicated enough to track what you're looking for: basically you're asking for grep -v ((.).+)\2{3}\1|([^0-9])\3{4}? Apr 19, 2014 at 19:05
• @PeterTaylor I would like to try to solve it without regex, though. Apr 19, 2014 at 19:10
• I had thought about regex, but I didn't think it would be that simple. Would adding more restrictions or banning regex help? Apr 20, 2014 at 1:18
• @Fraxtil, my opinion is that as a general rule if you need to ban the obvious way of doing something then you might as well just abandon the question. (With the exception, obviously, of banning libraries which are specifically designed to solve the same problem. Regex being a general tool rather than something designed for this specific problem don't fall into that exception). Apr 21, 2014 at 8:52
• @PeterTaylor, that's a good point. Maybe I'll revisit the idea later if I can find a way to make it more interesting. Apr 21, 2014 at 18:56
• I did make a decent question out of doing a basic regex problem without the use of regex (I should have, in hind sight, banned basic pattern matching as well as regexes...Bash shouldn't almost beat APL in sheer character count in a code golf). Apr 21, 2014 at 21:06
• @impinball "Bash shouldn't almost beat APL in sheer character count in a code golf" -- why? Apr 24, 2014 at 12:53
• Or at least in that context (tr is a pattern matching replace algorithm with regex like functionality). I would be a little more likely to accept Bash's builtin pattern matching expansion than tr. Apr 25, 2014 at 21:49

# Am I a Matroid?

## Input:

A list I that is a subset of the powerset of E={1,2,...,n} which represents the independent sets of elements of the purported matroid M=(E,I). Note that the cardinality of the ground set may be for the purposes of this question ignored. Any elements of E that appear in none of the elements of I cannot contribute (i.e. if M=(E,I) is a matroid then M=(E union K,I) is a matroid for any set K.

Input may be in whatever list format you desire, be it as simple as no separators but spaces (using 0 for the empty set): 0 1 2 3 12 13 or as complicated as whatever list literals are in your favorite language (such as python's: [[],[1],[2],[3],[1,2],[1,3]]).

## Output:

A variation on 1/0, true/false, yes/no answering the question: is M a matroid?

## Definition:

M=(E,I) is a matroid if:

1. I is not the empty set
2. If J is in I and K is a subset of J, then K is in I
3. If J,K are in I and |K|<|J| then there exists an element x that is in the set difference J-K such that K union {x} is in I.

There are equivalent formulations of condition 1 and 3, also there are conditions on the bases (maximal elements of I w.r.t. cardinality) that are equivalent to these. If people want I can post those too or leave them as optional research.

## Examples:

I={{},{1},{2},{1,2}} is a matroid.

I={} is not a matroid because it is empty (by axiom 1).

I={{},{1},{1,3}} is not a matroid because if it has {1,3} independent then it must have {3} independent (by axiom 2).

I={{},{1},{2},{3},{1,2}} is not a matroid because if it has {1,2} and {3} independent then it must have either {1,3} or {2,3} independent (by axiom 3).

I={{}} is always a matroid, as is I=powerset([1,2,...,n]) for any n>0 as they both trivially satisfy the axioms.

## Specs:

Submission is either a program taking input from standard input or command line argument or a function that takes I as input (as a string) and returns the specified binary answer. No upperbound on the size of input should be hardcoded.

I would intend for this to be a code-golf challenge.

• Rather than provide alternative definitions, just link the first mention of the word matroid to the Wikipedia page. May 5, 2014 at 11:59
• Hello! This looks like a good but abandoned meta post, would you be willing to offer it for adoption? (If you want to, you can still post to main.) Due to community guidelines, if you don't respond to this comment in 7 days I have permission to adopt this.
– user58826
Jun 9, 2017 at 16:38