Sandbox for Proposed Challenges

Question

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 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.

To post to the Sandbox, scroll to the bottom of this page and click "Answer This Question", or click on the "Add Proposal" link below. Click "OK" when it asks if you really want to add another answer. Write your challenge just as you would when actually posting it. 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.

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Answer 1

Sloppy Shuffle

Write a program that will shuffle the numbers from 1 to 52. Rather than from your language's random facility, the result will be determined by the input. But not in any particular way -- however you choose!

The Rules

• The program must accept all possible (finite) inputs. It doesn't matter if it is empty, or the result of monkeys with typewriters, or anything in between. Literally any input must be accepted without (unhandled) errors.
• For each of the 52-factorial possible ways of shuffling the numbers, there must be at least one finite input that will make your program produce this permutation.
• No matter what (finite) input is given to the program, it must produce some permutation of the numbers.
• If given the same input, the program must always produce the same permutation.
• Nothing should be produced on stderr.
• Standard restrictions apply.

Input/Output

Default input methods (such as stdin or command line args) are acceptable. If using stdin, any finite input from stdin must be accepted (although it doesn't all have to be read). For other input methods, use your best judgement in accepting arbitrary binary or string data as appropriate.

Default output methods (such as stdout) are acceptable. The form of the output should be the number from 1 to 52 in some order corresponding to the permutation as appropriate for your output method.

Scoring

This is code golf. The shortest answer in bytes wins!

However, in case of a tie in code length, the first tiebreaker is the maximum over all permutations of the minimum input length needed to generate that permutation. The program that has a larger minimum input wins.

(That may have been confusing, so an example: if program A can generate any permutation with no fewer than 100 bytes of input, but program B needs at least 1000 bytes to generate the identity permutation, program B wins the tie.)

Example

This is an example of a program which fulfills the requirements in Lua:

-- return a number from (1,n) depending on input
local function pick_from(n)
  local str = io.read() or ""

  -- always proceed even if input is not a number
  local num = math.floor(tonumber(str) or 0)

  -- guard in case of parsing overflow (e.g. input of 1e99999999999)
  if num ~= num or num > 1000 or num < -1000 then
    num = 0
  end

  return 1 + (num % n)
end

-- create a list of 52 numbers
local deck = {}
for i = 1, 52 do
  deck[i] = i
end

-- Fisher-Yates shuffle algorithm
for i = 52, 1, -1 do
  local j = pick_from(52)
  if i ~= j then
    deck[i], deck[j] = deck[j], deck[i]
  end
end

for i = 1, 52 do
  print(deck[i])
end

Notice that although I used the Fisher-Yates algorithm, the property that Fisher-Yates generates a permutation uniformly is irrelevant to the correctness of the program.

Another note -- if you never read at least log2(52!) bytes from the input, it is probably impossible for your program to generate all permutations.

Answer 2

How clean is my snow? code-golf

_{Idea shamelessly take from https://codereview.stackexchange.com/questions/118538/how-clean-is-my-snow#comment221029_118538}

---

The challenge

Your challenge is to tell how clean my snow is. Unclean snow is any snow that is not pure white. This would be super easy except for one hiccup, not all of the image is a picture of the snow, in the case of the image above some of the image is the sky (can't you tell? I'm such a good artist!).

Determining where the background is

[Write-up coming, it has to do with how large the splotch is and finding the biggest white spot, so the clouds don't count]

Answer 3

ToUpperCase... Mathematica style

For this challenge, you must write a program or function that converts every character in a string to upper case. "Wouldn't this be too broad/a duplicate/etc.?" you ask. Nope; you have to exactly implement Mathematica 10.1's ToUpperCase function!

Note

ToUpperCase works quite peculiarly on Unicode. For example, ß converts to SS! The full replacement list (from:to(,to);):

97:65;98:66;99:67;100:68;101:69;102:70;103:71;104:72;105:73;106:74;107:75;108:76;109:77;110:78;111:79;112:80;113:81;114:82;115:83;116:84;117:85;118:86;119:87;120:88;121:89;122:90;223:83,83;224:192;225:193;226:194;227:195;228:196;229:197;230:198;231:199;232:200;233:201;234:202;235:203;236:204;237:205;238:206;239:207;240:208;241:209;242:210;243:211;244:212;245:213;246:214;248:216;249:217;250:218;251:219;252:220;253:221;254:222;255:89;257:256;259:258;263:262;269:268;271:270;275:274;277:276;283:282;301:300;305:73;322:321;328:327;337:336;339:338;345:344;353:352;357:356;367:366;369:368;382:381;945:913;946:914;947:915;948:916;949:917;950:918;951:919;952:920;953:921;954:922;955:923;956:924;957:925;958:926;959:927;960:928;961:929;962:931;963:931;964:932;965:933;966:934;967:935;968:936;969:937;977:920;981:934;982:928;987:986;989:988;991:990;993:992;1008:922;1009:929;1013:917;8458:63350;8467:8466;8495:8496;8500:63358;63154:63344;63155:8492;63156:63346;63157:63347;63159:8497;63161:8459;63162:8464;63163:63353;63164:63354;63166:8499;63167:63357;63169:63359;63170:63360;63171:8475;63172:63362;63173:63363;63174:63364;63175:63365;63176:63366;63177:63367;63178:63368;63179:63369;63180:63370;63181:63371;63182:8493;63183:63373;63184:63374;63185:63375;63186:63376;63187:8460;63188:8465;63189:63379;63190:63380;63191:63381;63192:63382;63193:63383;63194:63384;63195:63385;63196:63386;63197:8476;63198:63388;63199:63389;63200:63390;63201:63391;63202:63392;63203:63393;63204:63394;63205:8488;63206:63396;63207:63397;63208:63398;63209:63399;63210:63400;63211:63401;63212:63402;63213:63403;63214:63404;63215:63405;63216:63406;63217:63407;63218:63408;63219:63409;63220:63410;63221:63411;63222:63412;63223:63413;63224:63414;63225:63415;63226:63416;63227:63417;63228:63418;63229:63419;63230:63420;63231:63421;63232:74;63488:63514;63489:63515;63490:63516;63491:63517;63492:63518;63493:63519;63494:63520;63495:63521;63496:63522;63497:63523;63498:63524;63499:63525;63500:63526;63501:63527;63502:63528;63503:63529;63504:63530;63505:63531;63506:63532;63507:63533;63508:63534;63509:63535;63510:63536;63511:63537;63512:63538;63513:63539;63572:63540;63573:63541;63574:63542;63575:63543;63576:63544;63577:63545;63578:63546;63579:63547;63580:63548;63581:63549;63582:63550;63583:63551;63584:63552;63585:63553;63586:63554;63587:63555;63588:63556;63589:63558;63590:63558;63591:63559;63592:63560;63593:63561;63594:63562;63595:63563;63596:63564;63604:63547;63608:63561;63609:63555;63614:63613;63616:63615;63618:63617;63620:63619;63621:63549;63622:63556;63626:63544;

Rules

• You cannot use a built-in that completely solves this challenge.
• If a function is written, the input is guaranteed to be a single string or equivalent.
• All characters not specified in the replacement list are to remain unchanged.
• All codepoints will be less than U+10000.
• If and only if your language can only take bytes as input, the string will be encoded in UTF-8.
• Standard loopholes are disallowed.
• Have fun!

Test cases TBD

Meta Questions

• What are some good test cases for this challenge?
• Is there something that I possibly missed while writing this challenge?

Answer 4

Use Simpson's Rule

Simpson's rule is a fairly simple method for approximating a definite integral of one variable. The idea is to approximate the function to be integrated by a series of interpolated parabolas, and then find the area under those.

As I learned in first-year calculus, the form of Simpson's Rule we'll be using is:

where the width of each interval is h.

Equivalently, this is the dot product with the vector h/3([1,4,2,4,...,1]) the same length as the input.

Input

• An array of n>1 real numbers representing the values of f at x-values equally spaced by h. n will be odd.

• h, a positive real number.

Output

The area approximation that Simpson's Rule gives.

Test cases

[0,0,0], 1 -> 0
[3,1,4,1,5], 1 -> 8

[add more]

Answer 5

Implement the Block Sort sorting algorithm

code-golf

Block sort is an interesting sorting algorithm (comparatively speaking). Here are some of its important properties:

• O(n log n) time complexity in worst and average case
• O(n) time complexity in best case
• O(1) space complexity (not including the space that holds the list itself)
• Stable

If you check out this table comparing sorting algorithms, you'll see that it's the only one that has the whole row highlighted in green.

Your challenge is to write an implementation of the block sort algorithm in the fewest bytes.

Answer 6

Advent of Code, puzzle 1

I don't know if anyone here spent their December working on the problems found on Advent of Code, but I thought some of the simpler problems might make good code golf puzzles.

So, here's the first one. There will be two challenges, and the solution should be a pair of programs, each of which solves one challenge.

Score is based on the combined byte count of the two programs.

(An alternative would be to also allow a single program that produces a tuple of the two solitions- what do you think?)

Input: An unbalanced string of open and close brackets.

Output 1: The count of the number of open brackets take away the number of close brackets.

Output 2: The index of the first close bracket that causes the running sum to reach -1.

Answer 7

Knights and Knaves posted

Undeleted so that comments are visible

Answer 8

Diopter lenses

In photography, there are thin lenses that you put in front of a photographic lens to make it behave like a close-up lens. Each of these lenses has an associated diopter value which is a positive integer. If you stack two (or more) of these lenses you get an equivalent of a lens with the diopter value that is the sum of the values of those lenses.

The problem

Your program should take one diopter value n as an input. The input need not be validated.

You should output in any human readable form a list of diopter lenses such that:

• the maximum diopter value you can form by stacking the lenses is n,
• every diopter from 1 to n can be formed by stacking a combination of those lenses,
• there exists no set of fewer lenses that complies to the above rules.

An example

Given the input of:

6

Print the output of

1
2
3

Because:

1=1
2=2
3=3
1+3=4
2+3=5
1+2+3=6

The rules

This is code golf, so the objective is to write the shortest possible code, but, since there is a trivial solution that might not be obvious to some, I suggest that the answer be encoded by some means so one wouldn't see the solution before attempting to solve the problem.

Any type of output is accepted, as long as the program outputs correct clearly separated positive integers and no other alphanumeric character.

My solution

python 2, 52 bytes, base64 encoded

bj1pbnB1dCgpCno9MQp3aGlsZSAyKnotMTxuOnByaW50IHo7eio9MgpwcmludCBuLXorMQ==

code-golf, optimization, combinatorics

Answer 9

Plotting Dynamical Systems in ASCII

code-golf

Input:

• A Function to and from the real plane (henceforth R2) , call it F

• A point in R2 that is to be the center of a disk, call it c

• A radius, call it r

• An integer representing the number of iterations to be performed, call it n.

Output:

You are to output n+1 ascii "images". The first depicts the disk D (with center c and radius r) and the ith image depicts F^i(D), aka F(...F( F(D) )...) where we have applied F to D, and then applied F to F(D) and so on until we have applied F i times.

Input Details:

• F will always be polynomial. See below for acceptable examples.

• Any c = (c1,c2) given will satisfy |c1|<50 and |c2|<25.

• Also, r will always be small enough that D the disk around c with radius r will contain no points with an x coordinate greater than 55 or less than -55 and no y coordinate greater than 32 or less than -32.

• n will be positive and less than 5.

Output Details

• We will be looking at a rectangular subset of R2 given by { (x,y) : -60 <= x <= -60 and -33 <= y <= 33}. i.e. a rectangle with side lengths 120 and 66 centered at the origin.

• Each output image will contain 320*320 characters. This represents the above region in R2 with gradations of 0.5 along each axis.

• Each character will represent a single point in R2. For example if we just look at part of the first quadrant (with the axes labeled which you need not do)

      y
      ^
      |
      .............................
    7 .............................
      .............................
    6 .............................
      .............................
    5 .............................
      .............................
    4 ............................
      .............................
    3 .............................
      .............................
    2 .....................b.......     b =(10.5,2)
      .............................
    1 ..a..........................     a = (1,1)
      .............................     z = (0,0)
    0 z............................  --------> x 
      0 1 2 3 4 5 6 7 8 9 | | | | |  
                        10| 12| 14
                          11  13

• Points that are empty (i.e. not in F^n(D)) will be represented by the . character, whereas filled spaces will be represented by #.

• Each image will have the same or fewer # represented points in it because we will not be displaying points that are outside the region.

  How do these maps work?

These are iterative maps we will be dealing with. For each point # in a given image, to get the next image, you will apply the given map F to it. If the point leaves the viewing area, you need not render it. However if in a later iteration it should reenter the viewing area, it should reappear.

For the purposes of this challenge, the image of a point should be rounded to the nearest 0.5.

A map might be F(x,y) = (4x(1-x), x+y)

Answer 10

Hourglass simulator

code-golf

Write a full program or function to simulate an hourglass.

Input

n, the number of seconds on the hourglass.

Behavior

At the start, there are n seconds on a timer, and the timer is counting down. When the user presses the spacebar with t seconds left, set the time left to n-t. Terminate the program when time runs out.

This models an hourglass where the top of the hourglass is initially filled with n seconds of sand. When the spacebar is pressed, the hourglass flips by 180°. When either side of the hourglass runs out of sand, the program terminates.

[Is there anything I'm missing? This spec seems really short.]

Answer 11

Implement an SR NOR latch with Life-like rules

code-challenge

In Conway's Game of Life, there exist meta-pixels that can have any Life-like rule. Consequently, it is possible to simulate Conway's Game of Life with itself. It is also possible to build circuit-like structures, such as wires and logic gates by mixing together different Life-like rules in the right ways.

For example, one can simulate wires with three Life-like rules: B/S, B1/S, and B2/S (where the original Game of Life has the rule B3/S23). In the gif below, which shows one way to cross parallel wires, these rules are black, blue/cyan, and green/yellow, respectively.

Building such circuit components is a fun challenge, and I encourage you to try a couple logic gates, like AND or OR.

The Task

Your task is to construct an SR NOR latch, the most fundamental latch in circuitry. From Wikipedia:

• If there is no signal on either R or S, leave the outputs unchanged.
• If there is a signal on R (reset), the Q output turns off and the Qbar output turns on.
• If there is a signal on S (set), the Qbar output turns off and the Q output turns on.
• You may safely assume you will never get a signal on both R and S at the same time.

Now, I used the word signal repeatedly because there are different ways to do wires. You can use the B1/S + B2/S combination shown above (blue and green, respectively), or you can use a B1/S12 rule like this:

These methods and others have their advantages and disadvantages. This is part of the challenge.

The Rules

• If periodic input/output is chosen, then the output should have the same period as the input. As one of the output wires will always be "on", the output from this should be periodic and infinite (like a glider gun, say).
• You may assume that periodic signals are given with a period greater than the time it takes for the latch to flip.
• Steady input must be succeeded by steady output.
• You may not make the field toroidal in any way, except for demonstration, like the wire crossing example above. This is intended to disallow cheating by wrapping vertically so no wire crossing is needed.
• If the circuitry is periodic, you may assume the input signal arrives at the most convenient time.
• Initially, the Q output should be off and the Qbar output should be on.

Scoring

Precise details on how to weight these is to be determined.

• Fewer rules is better. The wire crossing example above has three rules: B/S for black, B1/S for blue, and B2/S for green.
• Smaller is better. Area will be considered, as in the minimum bounding box needed to contain all necessary pixels that are not part of a wire. For instance, the wire crossing example above has a bounding box that is 4 pixels wide (the tips of the wires - where there is a blue cell without a green sheath - are not included) and 9 pixels high, for a total area of 36 pixels.
• Faster is better. For this, count the number of generations from when the input arrives to when a fully formed output leaves. For the example above, this would be 9 units of time. Here is a gif of those 9 generations, including the one before.
  
• Lower latency is better. I define this to be the number of generations after a fully formed output leaves until the system has either stopped evolving or settled into a periodic pattern. The example above would have a latency of 2 generations. For periodic patterns, "settled" is defined to be when the system reaches the first pattern that will be repeated (the start of the cycle).

Note: I strongly recommend using Variations of Life for this.

Meta

• Additional clarifications needed?

Answer 12

Dice sums from side values

I rolled some dice and put them on the table with their sides touching and forming one object with 8 horizontal sides. This means I put the dice in one of these formations (up to rotations):

xx   x
xx   xx  xxx

I read the number pips on the 8 horizontal sides in counter clockwise direction. You should write a program or function that given the list of the 8 horizontal sides in counter clockwise order returns a list of possible sums of the top pips from the dice rolling.

The layout of a die is always the following:

    +---+
    | 1 |
+---+---+---+---+
| 2 | 3 | 5 | 4 |
+---+---+---+---+
    | 6 |
    +---+

For example if the input is 3 2 1 1 2 6 6 5 there are four possible configurations with top views:

623, 633, 643, 653 giving the output list 11, 12, 13, 14

with the sides always being

 566
3XXX2
 211

For the input 1 1 2 2 3 3 2 2 there is only one configuration with the top view:

46
31 giving the one element output list 14

Input

Output

Examples

This is code golf so the shortest entry wins.

Related code golf with a single die: Determine dice value from side view

Answer 13

Length of a month starting from a specific day

Given a date, you are to output the number of days from today, to the last date that has a number less than today next month.

It can be calculated this way:

• If the current date in the month is not more than the number of days next month, output the number of days in the current month.
• Otherwise, output the number of days in the next month + number of days starting from the current day in the current month.

This is code-golf. Shortest code wins.

Examples

2016-01-21  ->  31
2016-01-30  ->  31
2016-01-31  ->  30
2016-02-29  ->  29

---

Should leap years be supported?

Answer 14

Repeatedly convert from minimal base to base 36

fastest-codebase-conversionrepeated-transformation

Your task is to convert an input of a list of strings which represent arbitrarily large numbers from the lowest possible base to base 36, repeatedly, until there is no further change to be made.

Rules:

• You may not use base conversion builtins.
• From 0 to 35 in base 36 is defined as:

  0, 1, 2, 3, 4, 5, 6, 7, 8, 9, a, b, c, d, e, f, g, h, i, j, k, l, m, n, o, p, q, r, s, t, u, v, w, x, y, z

• All submissions will be tested on this cloud 9 workspace and should be uploaded for testing (along with any updates) on this GitHub repository.
• All submissions must be written for compilers/interpreters that:
  • Are free to use.
  • Do not take up excessive space.
  • Can run with simple installations on Ubuntu 14.04.

Test Cases:

Coming soon

Answer 15

Elementary Cellular Automata, My Dear Watson code-golf

A seemingly innocent dinner party composed of elementary cellular automata has just been turned into a murder mystery. One of the cellular automaton guests has killed the host! All that remains as evidence for who committed the crime is the nth generation of the perpetrator. Luckily for them, Sherlock Holmes is on the case.

Show Watson how it's done by taking an integer n, and a string representation of the nth generation of the murderous automaton and printing or returning a list of the possible suspects (the numbers representing the rule of each amphichiral elementary cellular automata, see the bottom of the linked page.)

Rules:

• The input string will have length 2n+3 for the nth generation.
• The first character of the string represents the values on the infinite tape to the left, and the last character of the string represents the same for the right.
• Assume that the automata start with a single 1 in the center of a string of all 0s.

Example

Generation 0 of every automaton:

010

Notes:

• I don't have a reference implementation yet, nor have I created any examples.

Answer 16

Binary Arithmetic Using Unary Operators code-golf restricted-source

This is based off a game I was playing with a friend a few years back. How many different mathematical operators can you implement using only unary operators in your source*. We were able to implement most basic arithmetic in C, but for this challenge you can use any language.

* Except under certain conditions, see below.

Specifics:

All binary operators are disallowed, except under the following conditions:

• Binary comparison operators are allowed as long as one operand is a constant (e.g. you can do if (x == 0) or if (x) but not if (x == y))
• You may use binary assignment to load user input, only at the start of your code, or if you create a binary = method using these rules.
• You may assume that all variables are default-initialized to 0; if your language does not default-initialize variables, you are allowed to set them to zero only at the start of your code.

Additionally, please note the following:

• You do not have to write a complete program if your language supports functions/methods.
• You can use other operators from your source (e.g. your implementation of * could use your implementation of +)
• Standard library functions follow these rules too (e.g. you can use sqrt(x) but not mod(x, y))

Scoring:

Your score is determined by the formula [code size in bytes] / [number of operators implemented]. So for example, a 300-byte program that includes the functions +, -, and * would count as 300/3 = 100. Lowest score wins.

Answer 17

[title TBD]

code-golf

Input

An integer n between 1 and [currently 1652; TBD at the time of posting the comic], inclusive.

Output

The XKCD title for comic number n. (This is the text written above the comic panel, i.e. the text content of the <div id="ctitle"> element, not the title-attribute value of the img element. Here's a handy list, though the actual comic on xkcd.com will govern if it differs from what's on that list. However, the title is displayed in caps and smallcaps due to CSS, and you must output it in caps and lowercase (respectively).)

(If by the time the question is posted there's a comics with an ampersand-escaped character reference — I don't think there are any now — then I'll also add a caveat about how the output of your program should include the actual character, not the ampersand-escaped reference.)

Obviously…

I/O can be by any standard means and in any standard format. And no using the Internet to look up the title.

Answer 18

The overall task will involve extracting market data for various trading instruments (represented by unique symbols), applying some transformations and statistical functions, and displaying the results in a report.

Obtain the following QUOTES series from Bashoop: TYQUOTES, FVQUOTES

The quotes data is stored as a BBO. BBO stands for best bid/offer, which represents the best bid and ask (ask and offer are interchangable terms) in the market for a given instrument at any given time. At each timestamp it contains, in the following order: bid price, bid quantity, ask price, ask quantity

1. Calculate a VwMpt at each timestamp t for each instrument's QUOTES series VwMpt_t = bid_price_t + (ask_price_t-bid_price_t) * (bid_qty_t / (bid_qty_t+ask_qty_t))
2. Calculate a rolling correlation rho of VwMpt returns (first difference, i.e. derivative) sampled at 1 minute intervals with a lookback of 100 samples
3. On a webpage, display a plot of VwMpt substracted from the first sample (so the time series starts at 0) of both series on the same line chart, and below it plot the rho lined up along the same time axis. You may use a library like Flot or something similar.

To download a series with a series_id of FVQUOTES from a Bashoop instance located at 149.202.47.189:8080 you can: curl -s -d "series_id=FVQUOTES" -d "start_ts=0" -d "end_ts=1451606400000000" -d "compress=0" http://149.202.47.189:8080/series -X GET where start_ts and end_ts are micros send epoch. In this case we want the full history.

Answer 19

Parse default arguments

code-golf

Many languages have the concept of default/variable arguments. It basically means you can have a function that when given too few arguments, will fill in the missing arguments with specified values. For example, you can do the following in Python:

WARNING: THE BELOW EXAMPLE CODE IS NOT GOLFED. PROCEED AT YOUR OWN PERIL

def f(x="default string"):
  print x

This means that calling f("foo") will print "foo", but calling f() will print "default string".

Python also has a mechanism for handling too many arguments ("rest"):

def f(*stuff):
  for thing in stuff:
    print thing

You can of course also mix these:

def f(x, y="default string", *z):
  ...

Unfortunately, python (pre-3.5), being python, yells at you when you put a default argument before a non-default argument. That's silly. You guys are smart; you should be able to make that work.

Challenge

Write a program, function, or whatever that when given a string representing the arguments and values passed to them, will print each argument's resulting value.

• If there are too few arguments, the mandatory arguments should be applied first, then the rest of the values into the default arguments (left-to-right).
• If there are too many, apply all values to arguments, and the remaining into the "rest" argument.

I'm even confusing myself, just look at the test cases

Input

• a string, array, or other reasonable format representing the parameter declaration
• a string, array, or other reasonable format representing the values passed to the arguments

Output

• the resulting values of all the arguments, in a reasonable format.
  note: "reasonable format" will be defined later

Test Cases

Test cases will be in the following format:

{arg string}
{value string}
=> {output}

So, here they are

x, y, z
10, 2, 4
=> x:10, y:2, z:4

x=2, y
5
=> x:2, y:5

a, b="a", c, *d
3, 4
=> a:3, b:"a", c:4, d:[]

foo, bar=2, *baz
9, 3, "kqly", 5
=> foo:9, bar:3, baz:["kqly",5]

*x, y
"ha", 2, 3
=> x:["ha",2], y:3

Answer 20

Is this number random?: Round 2

The same as Is this number random?, but with 256 or 512 numbers in each category instead of 64; thereby making a modulo-chain infeasible to find. I hope this will encourage more interesting strategies.

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Is this enough of a difference from the existing question to merit a new one? Are there any other flaws with the distribution? Could I change this to require splitting into 4 or so buckets instead of 2?

Answer 21

Reverse Engineering

cops-and-robbers reverse-engineering code-golf

Cops

You must write a program or function in as few bytes that takes in an integer or a set of integers, performs a defined task on them (for example, finds the prime factorisation), and gives an integer or a set of integers as output. The number of integers in input and output will be pre-defined, so will be the task. You should provide appropriate limits for the variable sizes to be supported (1 bit, 1 byte, 2 byte etc.) and any additional conditions (0 not supported, N<100, M>N, etc.), and your program should work (atleast in theory, does not need to be time or memory efficient) for all possible inputs allowed by you.

You must also submit a reference code (ungolfed) in any language that performs the exact same process in reverse. Meaning, when given the output of the first program, it should be able to deduce the input given. This should be possible (atleast in theory) for all inputs accepted by you in the first program.

For example, suppose the first program takes in two 1-byte prime numbers m and n, and outputs all prime numbers between the two of them. Since the number of integers in input must be pre-defined (and not dependent on input), we state an additional rule that there will be a total of 60 integers in output, and if there aren't that many prime numbers, then zeros will be outputed.

Input to program 1: 23 41

Output from program 1: 29 31 37 39 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

Now the second program will perform the same process in reverse.

Input to program 2: 29 31 37 39 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0

Output from program 2: 23 41

Scoring

Robbers will attempt to golf the second program as much as possible. Your score is given by the ratio of bytes in the best golfed code by a robber and the bytes in your code. So if your code is 23 bytes, and a robber writes the code for the reverse process (in any language) in 102 bytes, then your score is 102/23. Your answer is deemed ineligible for scoring if it has negative score. Highest score wins.

Robbers

You must pick the second program submitted by a cop and attempt to golf it (in any language) as much as possible. You may submit a program or a function. You may use a different algorithm if you choose to, but the results must be exactly the same.

Scoring

????

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1. Is it ok to combine code-golf with cops-and-robbers like I have done?

2. What should the scoring criterion be for the robbers?

3. Is my challenge too generic (because it accepts way too many kinds of tasks)? If yes, what can I do about it?

4. Any further questions or suggestions are welcome. If you are sure of a suggestion being mandatory, you may make the edit yourself.

5. Are the tags ok?

Answer 22

Are bug hunts like this allowed?

Bug Hunt - Make a change in a Git repo that Git cannot detect

Challenge: In the working directory of a Git repo, make a change that Git cannot detect.

• Changes can be on any file in the working directory or subdirectories that is tracked by Git.
• You may use any tool to make the change, or script your own program to do so.
• For tools, state the tool used and the steps to reproduce.
• For script or program, produce the code (please use GitHub Gist if it's too long). State the language and compiler version, if any.
• You can also do the change manually. In this case, outline the steps.
• State the version and platform of the Git binary used.
• Show a comparison between an actual clean working directory and the modified one to show the change Git can't detect.
• Show that git status says "nothing to commit, working directory clean".

Winning Criterion:

• The extend of the undetected change - the bigger the change, the better.
• Reasonably latest Git version.
• Easy to reproduce.
• [Optional] Short code or simple steps. It's OK if it's not, as long as you do something exceptional.
• Most upvotes (for tiebreaker reasons).
• [Optional] You located an actual unfixed bug in the Git source code, and not just a quirk in something else.

Restrictions:

• Obviously, using .gitignore is not allowed. It's a bug hunt. Changes that Git is designed to ignore are not allowed. We should reasonably expect Git to see and report the change, but find that Git doesn't.
• Use latest Git version you can get. Some old version with some bug that's already fixed doesn't count.

Please let me know if this is OK, so I can go ahead to post it on the main site.

I could only find file-system. A suggested tag bug-hunt would have been the best.

Answer 23

Calculate the last N digits of Graham's Number

fastest-code

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Write a function or program that, given an integer x, outputs the rightmost x digits of Graham's Number.

Rules:

• You may not hardcode the answer in
• You may not fetch the answer from an external file or library

Scoring:

• Will be tested over 100 iterations on my machine with an average time given for different x values
• To Be Decided... (Input would be appreciated)

Answer 24

Paint the Mona Lisa in 1 KiB of code

** Oops, it seems that something like this has already been posted (and I didn't know about it before), but please read the last section below

This is my attempt to salvage this challange by Nathaniel, which was deleted after getting no less than 19 upvotes.

Here is a picture of da Vinci's Mona Lisa:

Your task is to reproduce the Mona Lisa in 1024 bytes or less. You will write a program or function that takes no input and loads no files, and outputs an image file.

The goal of this challenge is to produce an image that is as close as possible to the Mona Lisa above. The image must have the same resolution, and the similarity/difference will be measured by the root-mean-square deviation (at the color component level) between the two images. That will be the only criterion for the score, but people are still free to reward interesting answers by upvoting them (as always).

Your code (program or function) must obey the following restrictions:

• The code must be no more than 1024 bytes in total (counted in UTF-8 if you use funky characters)
• It must output the image in a standard uncompressed format such as BMP or PPM; the image can be written to the standard output or directly to a file
• The image must have the same resolution as the original - 215 by 320 pixels
• The code must be completely self-contained, taking no input and loading no files (other than importing libraries, which is allowed)
• You may not use built-in or library code that implements a decompression algorithm (unzip, unlzma, jpeg decompression etc). It is fine to use such algorithms if you implement them yourself within the 1024 byte limit.
• If your language or library includes a function that outputs the Mona Lisa, you are not allowed to use that either.
• It should run deterministically, producing the same output every time.
• Your code must be runnable in Linux using freely available software

It is possible that some submissions will themselves be generated by code. If this is the case, please include in your answer the code that was used to produce your submission, and explain how it works. The above restrictions do not apply to code used to create the code, they only apply to the 1024-byte code that produces the output image.

code-challengegraphical-output

TODO:

• provide code to calculate the score
• use a better-quality image?

Duplicate?

Well, some may argue that this is a duplicate of the Starry Night challenge, but I think it differs in at least 3 ways:

• uncompressed output
• no prewritten decompressor allowed
• UTF-8 byte count

Also, the image is not the same so it may not benefit from all the same techniques (I'm also open to using a different image altogether, such as the one from this other deleted challenge by Nathaniel).

If you have any other ideas how to improve the challenge, let me know.

Answer 25

Factorize Gaussian Integer

code-golfmatharithmeticcomplex-numbers

Given a nonzero gaussian integer your program/function should return the factorization of that integer g into prime factors pi and an unit u:

g = u * p1^e1 * ... * pk^ek

As the factorization is only unique up to units, we make following restrictions

• All primes should p should be in the first quadrant, that means that Re(p) > 0 and Im(p) ≥ 0.

• The unit should be represented as power of i. It should have the lowest nonnegative exponent.

• The primefactors should be sorted by the real part increasingly. If two real parts are the same, they should be sorted by imaginary part (also increasing.)

Examples

11-27i = i^2*(1+i)*(2+i)^2*(4+i)
2     = i^3*(1+i)^2

To be added: Examples, input output spec

https://en.wikipedia.org/wiki/Table_of_Gaussian_integer_factorizations

is_gaussian_prime(z)?

https://stackoverflow.com/a/2271645/2913106

Answer 26

Create a race condition

Your objective is to create program where concurrent threads race to produce a result. The program is simple. Print the sum of every element in the cartesian product of two sets.

An example of standard input would be

2 5 8 10 | 9 2 3 7 512 | 3 1 2 | 9 8 6 3

The program would then need to spin up two separate threads to calculate each result, and the first thread (and only the first thread) to complete should print "I WIN!" and the answer without using mutexes or other synchronization methods.

Rules

• You cannot use mutexes or synchronisation
• The operation must be run concurrently
• Standard input will contain any multiple of two sets, and the program should use (no of sets / 2) threads, as well as the main thread that spins everything.
• The order of execution on the slave threads is not important
• Some failure cases where more than one thread prints "I WIN!" is acceptable, but should be a rare case Sandbox comment: Not sure about verifying this one? or should not bother at all?

Sandbox comments

I saw the TCP Server question and I liked the idea of a challenge that is specifically difficult for golfing languages, and I was thinking about a few ideas for challenges that might work based specifically on parallel programming failures. I'm not sure if this one really fits the bill, hoping for suggestions to improve the challenege itself before refining the criteria.

Answer 27

A Tiny Raytracer

Your task is to make a tiny 2D raytracer to render beautiful ascii images.

Input

Your input will be an arbitrary 2D array delimited by newlines with the following structure

########
#9     #
#      #
#  ##  #
#  ##  #
#      #
#    ###
########

The symbols are: 0-9 = Light source = Emptiness # = Wall

Your expected output should look like this:

########
#987654#
#876543#
#76##32#
#65##00#
#543000#
#43000##
########

How Light Propagates

Light will travel in a straight line from lightsources through empty space and will be completely blocked by walls. Light falls off according to this function:

light_intensity = clamp(floor(9 - source_intensity * ||dist_to_lightsource||), 0, 9)

Where || || is the euclidean norm between the cell containing the light source and the cell in question, with 1 cell = 1 unit. All light intensity values are clamped to be between 0-9.

Light falls on an empty cell c whenever a straight line can be drawn from any part of c to the cell containing the light source without passing through a wall. For example, here I have all of the cells affected by a light source marked as *:

########       ########
####   #       ####***#
#9   #     =>  #****#  
###    #       ###****#
### ####       ### ####

Whenever there are multiple light sources, their contributions to the final light intensity are summed (and clamped to be between 0-9).

For example:

################
#9            6#
################

Should yield:

################
#98765432223456#
################

Rules

Standard code golfing rules. Input can have arbitrary size.

Fun Optional Bonuses

• Output the result as a graphical image.
• Support light values of between 0-255 (in this case columns of the input and output will be space delimited)
• Support colors (in this case light will be denoted by a standard 24-bit hex code 0xFFFFFF, and space delimited).

These don't give you any bonuses in the competition, but would be cool.

Answer 28

Self-decrypting code

code-challenge

The Caesar cipher is perhaps the earliest and most well known form of encryption. Here's a quick overview:

Pick a message, and a numerical encryption key. For this example, I'll pick "HELLO, WORLD" and 3, respectively.

First, convert each letter into its ASCII number:

H -> 72
E -> 69
L -> 76
L -> 76
O -> 79
, -> 44
[space] -> 32
W -> 87
O -> 79
R -> 82
L -> 76
D -> 68

Then, add the key (3) to each and convert back into a letter

75 -> K
72 -> H
79 -> O
79 -> O
82 -> R
47 -> /
35 -> #
90 -> Z
82 -> R
85 -> U
79 -> O
71 -> G

So the encrypted message is "KHOOR/#ZRUOG"

Your task

Write a full program that is a Caesar cipher-encrypted valid English message. The program must take no input and it will output the unencrypted version of itself.

Some rules:

• The program must be at least length 2.
• The key may not be 0, 32, or 256
• All of the code must be executed (no comments to arbitrarily extend code length).
• The Linux word list will be used to judge if a message is English. Words must be separated by ASCII character 32. Words can mix uppercase and lowercase.
• Your program does not need to be written in printable ASCII.
• File I/O is allowed, but only to read the source code file.
• No other standard loopholes.

Scoring

The submission with the longest message wins. Anything over 200 characters will be scored as exactly 200 characters. Ties are broken by upvotes.

Answer 29

Calculate the number of consecutive 0's at the end of n!

fastest-code

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Simply put, write a program or function that takes n and returns the number of consecutive 0's at the end of n!

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Examples

Input: 12
Output: 2

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Input: 12345
Output: 3082

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Input: 100000
Output: 24999

Answer 30

How many pixels are in each ASCII char?

code-golf

Write a program or function taking a single printable ASCII character as input that outputs how many pixels it takes to display that character to the screen.

Input can be taken by any reasonable method, including reading from a file, STDIN, or function argument. Input from a variable hardcoded into the program is not reasonable.

Output may by given by any reasonable method, including writing to a file and STDOUT. Extraneous output is permitted as long as the result remains unambiguous.

"Printable ASCII character" is defined as a character within the codepoints 32-126, inclusive.

A pixel counts as part of a character if the pixel is non-white after the character is written to a white screen.

The required font is Times New Roman, 20pt.

Do not hardcode the result.

Reference Solution: (JavaScript)

//create a canvas to display the character
var canvas = document.createElement("canvas")
canvas.width = 100
canvas.height = 100
document.body.appendChild(canvas)

var context = canvas.getContext("2d")

//make the canvas white
context.fillStyle = "white"
context.fillRect(0, 0, 100, 100)

//make the text black and set the font
context.fillStyle = "black"
context.font = "20pt Times New Roman"

//ask for the char
var char = prompt("Enter your ASCII char")
   
//draw the char
context.fillText(char,50,50)

//get the canvas pixel data
var pixelData = context.getImageData(0, 0, 100, 100).data
var pixelCount = 0
for(var i = 0; i < pixelData.length; i+=4) {

    //if the pixel isn't white, increment the counter
	if(pixelData[i] != 255 || pixelData[i+1] != 255 || pixelData[i+2] != 255) pixelCount++
}
alert(pixelCount)