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You need to produce output that is non-deterministic.

In this case, this will be defined to mean that the output will not always be the same result.

Rules:

  • A pseudo-random number generator that always has the same seed does not count.

  • You can rely on the program being run at a different (unknown) time each execution.

  • Your code's process id (if it's not fixed by the interpreter) can be assumed to be non-deterministic.

  • You may rely on web-based randomness.

  • Your code may not take non-empty input. Related meta post.

  • The program is not required to halt, but the output must be displayed.

Leaderboard

function answersUrl(a){return"https://api.stackexchange.com/2.2/questions/"+QUESTION_ID+"/answers?page="+a+"&pagesize=100&order=desc&sort=creation&site=codegolf&filter="+ANSWER_FILTER}function commentUrl(a,b){return"https://api.stackexchange.com/2.2/answers/"+b.join(";")+"/comments?page="+a+"&pagesize=100&order=desc&sort=creation&site=codegolf&filter="+COMMENT_FILTER}function getAnswers(){jQuery.ajax({url:answersUrl(answer_page++),method:"get",dataType:"jsonp",crossDomain:!0,success:function(a){answers.push.apply(answers,a.items),answers_hash=[],answer_ids=[],a.items.forEach(function(a){a.comments=[];var b=+a.share_link.match(/\d+/);answer_ids.push(b),answers_hash[b]=a}),a.has_more||(more_answers=!1),comment_page=1,getComments()}})}function getComments(){jQuery.ajax({url:commentUrl(comment_page++,answer_ids),method:"get",dataType:"jsonp",crossDomain:!0,success:function(a){a.items.forEach(function(a){a.owner.user_id===OVERRIDE_USER&&answers_hash[a.post_id].comments.push(a)}),a.has_more?getComments():more_answers?getAnswers():process()}})}function getAuthorName(a){return a.owner.display_name}function process(){var a=[];answers.forEach(function(b){var c=b.body;b.comments.forEach(function(a){OVERRIDE_REG.test(a.body)&&(c="<h1>"+a.body.replace(OVERRIDE_REG,"")+"</h1>")});var d=c.match(SCORE_REG);d?a.push({user:getAuthorName(b),size:+d[2],language:d[1],link:b.share_link}):console.log(c)}),a.sort(function(a,b){var c=a.size,d=b.size;return c-d});var b={},c=1,d=null,e=1;a.forEach(function(a){a.size!=d&&(e=c),d=a.size,++c;var f=jQuery("#answer-template").html();f=f.replace("{{PLACE}}",e+".").replace("{{NAME}}",a.user).replace("{{LANGUAGE}}",a.language).replace("{{SIZE}}",a.size).replace("{{LINK}}",a.link),f=jQuery(f),jQuery("#answers").append(f);var g=a.language;g=jQuery("<a>"+g+"</a>").text(),b[g]=b[g]||{lang:a.language,lang_raw:g,user:a.user,size:a.size,link:a.link}});var f=[];for(var g in b)b.hasOwnProperty(g)&&f.push(b[g]);f.sort(function(a,b){return a.lang_raw.toLowerCase()>b.lang_raw.toLowerCase()?1:a.lang_raw.toLowerCase()<b.lang_raw.toLowerCase()?-1:0});for(var h=0;h<f.length;++h){var i=jQuery("#language-template").html(),g=f[h];i=i.replace("{{LANGUAGE}}",g.lang).replace("{{NAME}}",g.user).replace("{{SIZE}}",g.size).replace("{{LINK}}",g.link),i=jQuery(i),jQuery("#languages").append(i)}}var QUESTION_ID=101638,ANSWER_FILTER="!t)IWYnsLAZle2tQ3KqrVveCRJfxcRLe",COMMENT_FILTER="!)Q2B_A2kjfAiU78X(md6BoYk",OVERRIDE_USER=34718,answers=[],answers_hash,answer_ids,answer_page=1,more_answers=!0,comment_page;getAnswers();var SCORE_REG=/<h\d>\s*([^\n,<]*(?:<(?:[^\n>]*>[^\n<]*<\/[^\n>]*>)[^\n,<]*)*),.*?(\d+)(?=[^\n\d<>]*(?:<(?:s>[^\n<>]*<\/s>|[^\n<>]+>)[^\n\d<>]*)*<\/h\d>)/,OVERRIDE_REG=/^Override\s*header:\s*/i;
body{text-align:left!important}#answer-list,#language-list{padding:10px;width:400px;float:left}table thead{font-weight:800}table td{padding:5px}
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    \$\begingroup\$ @mbomb007 In C there are many things that are simply "undefined" behaviour. Any given interpreter is allowed to do whatever it wants in any situation. For all we know, gcc might order you a pizza if you try to overflow a signed integer on a rainy Tuesday, but will make a trout jump out of your screen on all other days. So you wouldn't really ever know if it's actually deterministic or not in any given implementation. \$\endgroup\$ – Martin Ender Nov 30 '16 at 20:44
  • 13
    \$\begingroup\$ @MartinEnder I'm not sure if that matters. We define languages here by their implementation, not by the specification (as languages without an implementation is not allowed) \$\endgroup\$ – Nathan Merrill Nov 30 '16 at 21:00
  • 2
    \$\begingroup\$ @MartinEnder Yeah, I agree with Nathan. \$\endgroup\$ – mbomb007 Nov 30 '16 at 21:01
  • 8
    \$\begingroup\$ Note that undefined behaviour in C often leads to crashes, and crashes on UNIX and Linux lead to core files which contain the process ID inside them. That would seem to comply with the question as currently worded. \$\endgroup\$ – user62131 Nov 30 '16 at 21:23
  • 5
    \$\begingroup\$ Unless I misunderstood, the question did not ask for code that takes advantage of undefined behavior. It asks for code that takes advantage of defined behavior to guarantee non-determinism. \$\endgroup\$ – WGroleau Dec 1 '16 at 3:30

116 Answers 116

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1
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C (gcc), 63 54 bytes

main(){int a;for(char*b;a=3;b++)for(;a;a--)printf(b);}

Try it online!

I can't even remember how this one works.

Down to 54 bytes by 2x-1.

Puts instead of printf creates triangle patterns instead, but I think they're boring.

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1
  • 1
    \$\begingroup\$ 54 bytes \$\endgroup\$ – user100947 Feb 26 at 10:02
1
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Julia, 4 bytes

rand

Try it online!

time

Try it online!

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0
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Shellscript (as implemented by ttyrec), 0 bytes

OK, here's a version of this idea that uses an interpreter that can actually be programmed with.

The ttyrec command by default just passes everything it sees on standard input to a shell, and thus obeys our definition of a programming language (it's Turing-complete, because bash is; it's basically just an alternate front-end to bash, and so is basically a shellscript interpreter that can be used to program with). However, it also creates a file ttyrecord containing a recording of the shell's output, and that file starts with the current time, in binary (and is also affected in some ways by the system's CPU and swapping load, as it tries to separate the output into frames). Thus, it produces a file with nondeterministic content as output.

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2
  • \$\begingroup\$ I'm not using any commands. Shellscript is Turing-complete. At least one implementation of it produces nondeterministic output in addition to running the program given, thus you get the output you want even with no commands. Languages are defined by the interpreter here. \$\endgroup\$ – user62131 Nov 30 '16 at 20:56
  • \$\begingroup\$ (the above was in reply to a since-deleted comment that this wasn't valid due to not using commands) \$\endgroup\$ – user62131 Nov 30 '16 at 21:03
0
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JavaScript, 8 bytes

Date.now

This evaluates to a function whose return value is nondeterministic, and conveniently doesn't actually need to be bound to anything specific to work.

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2
  • \$\begingroup\$ Basically, this is the same as the Date answer. \$\endgroup\$ – Ismael Miguel Nov 30 '16 at 23:20
  • \$\begingroup\$ @IsmaelMiguel I did have the idea of returning a builtin first; I just returned the wrong builtin. \$\endgroup\$ – Neil Dec 1 '16 at 0:31
0
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Batch, 6 4 bytes

time

Needs to be run with <nul which is apparently permissible.

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2
0
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Swift 3, 13 bytes

print(Date())
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0
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QBIC, 4 bytes

?_r|

This generates and prints a random number between 0 and 10. QBIC uses the classical RANDOMIZE TIMER at the start of execution to set the RNG.

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0
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Actually, 1 byte

G

Try it online!

Good old rand(). In Python 3, 2500 random bits from the system's cryptographically-secure randomness source (getrandom() for Linux, /dev/urandom for *NIX, or CryptGenRandom for Windows) are used for the seed, falling back on the current UNIX time (as precisely as possible for the given platform - at minimum, 1-second precision) if such a source of randomness is not available.

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0
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Microscript, 2 bytes

r9

Produces a random integer on [0,8]

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0
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Mouse2002, 7 bytes

&RAND !
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0
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Microscript II, 1 byte

R

Produces a random 64-bit float on [0,1).

Another one-byte solution would be C, which produces a new continuation object, whose timestamp (which the reference implementation includes in its string representation) will be nondeterministic.

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0
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HSPAL, 18 bytes

26FFFF
400000
120000

Prints a random 16-bit integer.

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0
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Math++, 5 bytes

$rand

Produces a random 64-bit float

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0
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ASP VBScript, 43 bytes

<%=createobject("scriptlet.typelib").guid%>

Outputs a unique ID like {52076580-3151-4EE7-AAFD-D975CD141EE4} based on current date/time.

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0
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C, 22 bytes

f(){putchar(time(0));}
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2
  • \$\begingroup\$ OP indicates in the comments that a full program is not needed and a function will suffice. Might I suggest replacing main with f to save 3 bytes? \$\endgroup\$ – Albert Renshaw Apr 11 '17 at 19:48
  • \$\begingroup\$ yes i replace main with f... thank you and a good day \$\endgroup\$ – user58988 Apr 12 '17 at 5:18
0
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Chip-8, 4 bytes

0xCFFF 'RND vF,FF
0xFF18 'LD ST,vF

This plays a sound for between 0 and 4.25 seconds. The seed always starts at 0, but it updates during the display interrupt which has a tiny chance of happening before the randomizer call, I hope.

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0
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Pyt, 1 byte

ɽ

Returns a random 32-bit integer.

Also 1 byte: ɹ, .

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2
0
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Gol><>, 3 bytes

x1h

The 'x' is a randomizer for the direction of the pointer, the 1 pushes a 1, and the h outputs and halts.

Try it online!

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2
  • \$\begingroup\$ You can also do Sxh to print a random float between 0 and 1 \$\endgroup\$ – Jo King Mar 1 '19 at 2:31
  • \$\begingroup\$ @JoKing I didn't think of that, thanks for pointing that out. that works as well. Though I don't think there is a smaller version of this \$\endgroup\$ – KrystosTheOverlord Mar 1 '19 at 2:57
0
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Pxem (Filename: 5 bytes; Contents: 0 byte)

  • Filename: x.r.n
  • File content is empty.

Explaination

  • x pushes an ascii code of the character (120) as a signed integer.
  • .r pops 120 to push back one of 0-119.
  • .n pops the integer to output as a decimal.
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0
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05AB1E, 2 bytes

Any program matching /^[ATт₁-₆]Ω|ž[a-g]$/ will give nondeterministic output. There are, of course, infinitely many programs that can do this, but these are all the two-byters. Unfortunately, I could not find a one-byter... :(

Try them online!

Explanation

The ones starting with ž are constants. The ones used here are time constants - ža, žb, žc, žd, že, žf, and žg are hours, minutes, seconds, microseconds, day, month, and year, respectively. The ones ending in Ω pick a random element (for lists), character (for strings), or digit (for integers) from top of stack. The one-byte commands that I could find that push something with more than one distinct element/character/digit were A, T, т, , , , , , and , which push abcdefghijklmnopqrstuvwxyz, 10, 100, 256, 26, 95, 1000, 255, and 36, respectively.

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0
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ThumbGolf, 4 bytes

Machine code:

de78 de20

Assembly:

        // Include ThumbGolf wrapper macros
        .include "thumbgolf.inc"
        .globl main
        .thumb_func
main:
        // Read random integer into r0
        rand    r0 // udf #0170
        // Print to stdout in base 10
        puti    r0 // udf #0040
        // Not required to exit, so just crash

Internally, ThumbGolf uses /dev/urandom, so this is guaranteed to be nondeterministic.

Alternative version, 2 bytes

Machine code:

de21

Assembly:

        // Include ThumbGolf wrapper macros
        .include "thumbgolf.inc"
        .globl main
        .thumb_func
main:
        // print address of argv
        // printf("%i", (int)argv)
        puti    r1 // udf #0041
        // exit by crash

Prints the memory address of argv which is almost guaranteed to be dynamically allocated, and therefore, nondeterministic.

However, it is context sensitive unlike the 4 byte solution.

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  • 1
    \$\begingroup\$ Non-competing status shouldn't be used nowadays. Answers in languages newer than the question are allowed, obviously considering that you don't hardcode the answer to the challenge into the language's interpreter and submit a 0-byter (or similar). That is already a standard loophole. \$\endgroup\$ – Makonede Feb 6 at 23:51
  • \$\begingroup\$ Also just realized; your two-byter is Þ! in Unicode. :P \$\endgroup\$ – Makonede Mar 2 at 22:49
0
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Phooey, TIO version, 4 bytes

<2$i

Try it online!

Abuses a bug to print the frame pointer.

This is because the tape does not wrap, so the tape just underflows to the stack.

<2 moves the pointer 16 bytes back, $i prints as an integer.

Very dependent on the version of the binary.

Phooey, proper version, 5 4 bytes

~t$i

Try it online!

~t stores the Unix time to the tape, and I already explained $i.

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0
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CSASM v2.2.1.2, 39 bytes

func main:
extern Random.Next
print
ret
end

CSASM has a built-in System.Random object that gets initialized to new System.Random() when CSASM.Core.Sandbox.Main(System.Reflection.MethodInfo, int, string[]) is called.

The default System.Random constructor initializes the seed to Environment.TickCount, which is different every time the executable runs.

extern Random.Next calls Random.Next() on the aforementioned object, which returns a positive int value.

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0
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EmojiCoder, 44 bytes

🙈🔢🌚🌝🌚🌚🌚🌚🌚🌝
✋

Try it online!

Push some random integer between 0 to 65 (chosen randomly) and output top of stack.

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0
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Barrel, 2 bytes

|n

Gets a random integer with | and prints it as a number with n.

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0
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.mmo (MMIX executable), 128 120 bytes

(xxd --jelly)

00000000: 98090100 98010001 00000100 e3ff0130  Ƭµ¢¡Ƭ¢¡¢¡¡¢¡ẉ”¢0
00000010: 00000103 e3ff0140 00000303 e3ff0140  ¡¡¢¤ẉ”¢@¡¡¤¤ẉ”¢@
00000020: e0012000 87000100 ef00a0a0 eb004040  ṭ¢ ¡⁷¡¢¡ṁ¡ɦɦḟ¡@@
00000030: a7000100 00000601 98020008 00000150  ʂ¡¢¡¡¡©¢Ƭ£¡®¡¡¢P
00000040: 00000000 00000002 20000000 98020008  ¡¡¡¡¡¡¡£ ¡¡¡Ƭ£¡®
00000050: 00000002 2f646576 2f72616e 646f6d00  ¡¡¡£/dev/random¡
00000060: 980a00ff 00000000 00000100 980b0000  Ƭ½¡”¡¡¡¡¡¡¢¡Ƭ¿¡¡
00000070: 00000000 980c0001                    ¡¡¡¡Ƭ€¡¢

Outputs two random characters in range @-_ to stdout.

Explanation

98090100 lop_pre 1,0                    (preamble, mmo v1, 0 tetras)
98010001 lop_loc 0,1                    (next tetra says where to load)
00000100 (256)
E3FF0130  SETL  $255,random
00000103  TRAP  0,Fopen,3               (open fd 3 for bin read from /dev/random)
E3FF0140  SETL  $255,data
00000303  TRAP  0,Fread,3               (read two bytes of data)
E3FF0140  SETL  $255,data               (set up $255 for writing it back out)
E0012000  SETH  $1,#2000                (we know where the data is)
87000100  LDWU  $0,$1,0                 (read those bytes from memory)
EF00A0A0  ANDNL $0,#A0A0                (ensure C0 control or @-_)
EB004040  ORL   $0,#4040                (ensure @-_)
A7000100  STWU  $0,$1,0                 (write them back to memory)
00000601  TRAP  0,Fwrite,StdOut         (write two bytes out)
98020008 lop_skip 8                     (encodes the next two tetras)
          TRAP  0,Halt,0                (halt)
         random OCTA fname              (argument 1 of fopen: ptr to filename)
00000150  (cont)
00000000  OCTA BinaryRead               (argument 2: mode)
00000002  (cont)
20000000 data OCTA Data_Segment         (argument 1 of fread/fwrite: buffer addr)
98020008 lop_skip 8                     (encodes cont + start of next)
          OCTA 2                        (argument 2: amount)
00000002  (cont)
2F646576 fname BYTE "/dev"
2F72616E  BYTE "/ran"
646F6D00  BYTE "dom\0"
980A00FF lop_post 255                   (one global register)
00000000
00000100                                (start at 0x100)
980B0000 lop_stab                       (symbol table)
00000000                                (no symbols)
980C0001 lop_end 1                      (one symtab tetra)

Basically, this reads two characters from /dev/random, then, after a bit of munging to ensure they're printable, dumps them to stdout.

I also used lop_skip to cut two tetras from the code.

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