This is the robbers' thread. The cops' thread is here.

Your challenge is to crack a cop's submission by finding an input that makes it halt. You don't have to find out why, or all inputs that make it halt if there's more than one, or the input the cop intended, just one input will do.

Once you have cracked a submission, post a link to it in a comment or edit to the cop's post. You can also flag your submission for a mod to edit it in the cop's post. Also, post the input used and a link to the cop's post in an answer in this thread. The robber that cracks the most submissions wins.

Multiple people can post cracks to the same cop submission, as long as they are different.

(If SE converted your duplicate answer to a comment, you may want to vote on this feature request)

Looking for uncracked submissions?

fetch("!.Fjs-H6J36vlFcdkRGfButLhYEngU&key=kAc8QIHB*IqJDUFcjEF1KA((&pagesize=100").then(x=>x.json()).then(data=>{var res = data.items.filter(i=>!i.body_markdown.toLowerCase().includes("cracked")).map(x=>{const matched = /^ ?##? ?(?:(?:(?:\[|<a href ?= ?".*?">)([^\]]+)(?:\]|<\/a>)(?:[\(\[][a-z0-9/:\.]+[\]\)])?)|([^, ]+)).*[^\d](\d+) ?\[?(?:(?:byte|block|codel)s?)(?:\](?:\(.+\))?)? ?(?:\(?(?!no[nt][ -]competing)\)?)?/gim.exec(x.body_markdown);if(!matched){return;}return {link:, lang: matched[1] || matched[2], owner: x.owner}}).filter(Boolean).forEach(ans=>{var tr = document.createElement("tr");var add = (lang, link)=>{var td = document.createElement("td");var a = document.createElement("a");a.innerText = lang;a.href = link;td.appendChild(a);tr.appendChild(td);};add(ans.lang,;add(ans.owner.display_name,;document.querySelector("tbody").appendChild(tr);});});
<html><body><h1>Uncracked Submissions</h1><table><thead><tr><th>Language</th><th>Author</th></tr></thead><tbody></tbody></table></body></html>

  • 2
    Does different mean different inputs (say, all inputs ending with 2 crack the cop's post - can you different people post different numbers ending in 2?) or different families of inputs, or different types of inputs? – Stephen Jul 24 '17 at 17:03
  • 1
    Multiple people can post cracks to the same cop submission... Please define different. – Dennis Jul 25 '17 at 13:41
  • @NoOneIsHere – programmer5000 Jul 25 '17 at 15:26

136 Answers 136

Malbolge, Doorknob

Try it online (Thanks Dennis!)

Input for Windows: F_⌠1234567890

Input on Linux based system using ISO-8559-1: F_ô1234567890

The heart of how the Malbolge program worked is that it depended on a behavior of the Malbolge interpreter which causes an infinite loop if it encounters any instruction which is not between 33 and 126. The program was constructed such that your input would allow you to modify a single instruction.

I modified the interpreter to dump the program memory state at the beginning of execution and to also produce 'normalized' source code which takes the form of a list of op codes that will be run during the execution of the program. With that information you could (slowly) determine that even though the program took 13 inputs only the 1st and 3rd inputs actually mattered.

Looking through the normalized code and memory dump (and a touch of debugger help) I devised the following:

a = op(input 1, 29524)

b = op(input 3, a)

c = op(486, b)

d = op(c, 37)

e = d/4 + d%3 * 3^9

e must be between 33 and 126

Where op is the so called tritwise "op" that is described in the specification. Using this information you can write a simple program which iterates over the possible inputs (0 to 255) and finds all solutions which meet the above criteria. I had found 2219 possible solutions, some of which will probably not be working solutions (you can't input the required characters). Specifically the above inputs are based on the solution:

(Input 1 = 70, Input 3 = 244)

  • I don't have the rep to comment cracked on the cops post. Could someone do that for me? – KBRON111 Jul 27 '17 at 2:23
  • 4
    Welcome to PPCG! Good job! I think with this crack, you'll soon have enough rep :) – Stephen Jul 27 '17 at 2:33
  • 1
    I commented across. And yes, excellent work; I was half expecting Malbolge to last the week! – Veedrac Jul 27 '17 at 2:34
  • 6
    Nice work! TIO uses UTF-8, but by wrapping it in Bash, your crack can still be verified.… You don't seem to need anything but F_ô by the way. – Dennis Jul 27 '17 at 5:07
  • 1
    Now I can sleep again – Juan Tonina Jul 27 '17 at 12:58

JavaScript (in Browser)


This is falsy, surprisingly

Edit: why is document.all falsy?

  • 4
    I'm speechless. – Dennis Jul 25 '17 at 16:34
  • 2
    Aahh... javascript, where everything is weird – Juan Tonina Jul 25 '17 at 16:36
  • 1
    Yes! That's the only correct answer here! – tsh Jul 26 '17 at 1:33

JS (ES6), Juan Tonina


Took a bit of looking in to find. Basically, +0 === -0 since === checks them as numbers, and 0 is finite, but sees +0 and -0 as different objects. Very smart cop :)

Try it online!

  • Ninja got it while I was logging in. Shoot. – user3033745 Jul 24 '17 at 16:59
  • Damn, solved faster than the time I spent thinking about the code :D – Juan Tonina Jul 24 '17 at 17:02

Python, Siphor

class A:
    i = True
    def __eq__(self, a):
        self.i = not self.i
        return self.i

a = A()

We just redefine equality to behave exactly as required to get the program to terminate.

  • Although I suppose I could have just defined __eq__ to raise... – g.rocket Jul 24 '17 at 21:35
  • I was about to submit with just returning 0 :p – Jonathan Allan Jul 24 '17 at 21:40
  • @JonathanAllan How does that work? – g.rocket Jul 24 '17 at 21:41
  • 1
    Pretty sure just class A:__eq__=lambda s,o:0 and f(A()) does the job. – Jonathan Allan Jul 24 '17 at 21:41
  • 1
    Ah yeah need the negation >_< – Jonathan Allan Jul 24 '17 at 21:42



Any number less than 0 works.

Try it Online!

JavaScript (ES7), Arnauld


"8e7" is solution

var crack_me = (x=0)=>{for(;~x/x.length**3!=-2962963;);}

var key = "8e7"

console.log("stopped :)")


No need to calculate this number, we can redefine length property

This sets ~x/x.length**3!=-2962963 to false

var crack_me = (x=0)=>{for(;~x/x.length**3!=-2962963;);}

var key = {toString:()=>"2962962",length:"1"}

console.log("stopped :)")

Operators priority

~ bitwise not is first

** exponentiation second

/ division third

JavaScript (Node.js), Adnan

[] and [] seem to work. I tried a bunch of them including null, undefined, NaN...

[] >= [] && [] <= [] && [] != [] evaluates to true.

Moral of the story: JavaScript is weird.

Try it online!

  • Yep, arrays are just objects. – programmer5000 Jul 24 '17 at 18:05
  • And objects are cast to strings for these types of comparisons. – Conor O'Brien Jul 24 '17 at 20:49

PHP, Sisyphus

(-0[0)> deal with it=1

The parse_str function changes the spaces and other characters to underscores. If you put a [ used for Array delimiter without closing, it changes it to an underscore but has the effect of not translating the following spaces (I don't know why).

Try it online!

  • WTF?! That is insane... – Veedrac Jul 25 '17 at 16:49

Bash, Veedrac


Try it online!

From the manpage:


If set (to any value), causes the program to list its dynamic dependencies, as if run by ldd(1), instead of running normally.

  • I thought this would last longer! Excellent work. – Veedrac Jul 25 '17 at 13:09
  • 1
    @Veedrac: I guess since you specified bash, it's unlikely that you'd find a statically-linked (e.g. busybox?) /bin/yes, but that is possible, in which case this env var would be ignored. – Peter Cordes Jul 27 '17 at 10:35

Mathematica, JungHwan Min


No clue whether this is the intended solution, but it passes in an expression that doesn't get evaluated until it's referenced as # inside the function, which will cause it turn return from the function immediately without doing any further evaluation. You can see that the function is actually called (instead of just throwing the exception before even invoking the function) by changing the function to:


Which will indeed print the stop before throwing the error.

  • Bingo! (I was actually going for Unevaluated[Abort[]], but same thing.) – JungHwan Min Jul 25 '17 at 15:29

Retina, PunPun1000


Try it online!

Any input with n 1s where the sum of the divisors of n+1 is equal to n+1 should work.

  • Nice to see someone get the intended solution – PunPun1000 Jul 24 '17 at 16:52



without newline. 3.send('exit') surely isn't equal to 5, but it executes Kernel#exit:

Initiates the termination of the Ruby script by raising the SystemExit exception

It's possible to call exit on 3 because:

The Kernel module is included by class Object, so its methods are available in every Ruby object [as private methods].

abort also works:

Terminate execution immediately, effectively by calling Kernel.exit(false). If msg is given, it is written to STDERR prior to terminating.

JavaScript (Node.js), programmer5000

Already cracked, but mine is slightly different :) Don't have enough rep to comment over in the cops. Also feel free to edit to fix formatting, my first post here.

Mainly I set __proto__ equal to a function that throws. Taken from looking at the Mozilla page for proto. (Sorry, low rep, can't post a link.)

x = {}
let No = function () { throw 'halted' }
x.__proto__ = new No()
f = x=>{while(x.__proto__);}

Try it online!

EDIT: Got some rep, so here's the link: Mozilla __proto__

  • I commented on the cop for you. – Stephen Jul 24 '17 at 23:03
  • 1
    Thanks! Also thanks all for the ups, guess I can comment now! – Haumed Rahmani Jul 24 '17 at 23:15
  • 1
    Welcome to PPCG :D – Conor O'Brien Jul 24 '17 at 23:22

Bash, Sisyphus

kill 0

Fortunately, kill is a shell builtin.

Try it online!

R, Jarko Dubbeldam


First time contributing anything, so do call out any mistakes I've made in format.

Pretty sure this is valid. Just a rewrapping of is.list(), right?

  • Incidentally, I don't have the rep to comment on the original so a hand would be appreciated if it's valid. – CriminallyVulgar Jul 27 '17 at 12:59
  • Commented for you. – TheLethalCoder Jul 27 '17 at 13:02
  • Not the intended solution, but works. Good job. – JAD Jul 27 '17 at 13:04

Javascript, programmer5000

Max string length

Uses a string with a length one less than what your engine supports. When adding "h" to this string, an error is thrown. Try it online!

function getAlmostMaxLenStr() {
  var prevBases = [];
  var base = "a";
  try {
    while(true) {
      base += base;
  } catch(e) {}
  for (var i = prevBases.length-1; i>=0; --i) {
    try {
      base += prevBases[i];
    } catch (e) {}
  return base;

Cross-origin block

Heavily inspired by the answer from @jadkik94, but works everywhere. Creates a cross-origin iframe, then passes the .contentWindow of said iframe. This fails when the function tries to use the value due to cross-origin safety.

let f=x=>{
  try {
    console.log(x+"h"); // we don't want to lock up your browser, do we ;)
  } catch (e) { console.log("Halted!\n",e); }
let iframe=document.createElement("iframe");
const url ="google") === -1 ? "" : "";

Primitive value

Variant of the .toString() answers - this just uses toPrimitive instead. It returns an object as the primitive value, which Javascript doesn't know how to handle (so it throws an error). Try it online!

  [Symbol.toPrimitive](){return {}}
  • Nice job, but still not intended solution! Very clever! – programmer5000 Jul 25 '17 at 11:30

JavaScript (Babel Node), Conor O'Brien

(Repost, accidentally put in cops.) Not sure what was intended but positive decimals that aren't enormous all seem to work.

Also I guess I still can't comment in Cops.


Try it online!

  • Forgot about that as well, good one. – Conor O'Brien Jul 24 '17 at 23:48

Javascript (NOT node.js), programmer5000

This can't be added because it creates an object that has no toString because a new Set does not inherent prototypes from from Object.


new Set()

Try it online!

  • This was probably the intended solution, I'll keep that in the bag of my head from now on :P – Stephen Jul 24 '17 at 20:29
  • Sorry this doesn't seem to work for me? Try it online! – Haumed Rahmani Jul 25 '17 at 1:04
  • @HaumedRahmani added a try online button. I used spider monkey, not babel. – Grant Davis Jul 25 '17 at 1:40
  • Not the intended solution, but nice job! – programmer5000 Jul 25 '17 at 1:49

Bash 4.2, Dennis


Clearly not the intended solution, because it works on newer bash as well.

Try it online.

Octave, Stewie Griffin

Input: exit

Reasoning: input evalutes whatever is input. exit exits the program.

Try it online!

Python 2, Foon


What it says on the tin, basically.

Try it online.

  • Interestingly enough, on TIO this times out for me; under Windows (specifically with winpty python and pasting in the line), it does exit as desired... and yeah, not surprisingly my schtict was exploiting the "input under Python 2 does eval under the hood" bit – Foon Jul 25 '17 at 11:01
  • @Foon Hmm, it's working fine on TIO for me. See link in answer. – Veedrac Jul 25 '17 at 11:18
  • Weird... I must have hit play and then typed input on my TIO link and not realized it – Foon Jul 25 '17 at 13:42
  • I'm pretty sure this cracks every python submission.. – enderland Jul 26 '17 at 3:13
  • @enderland Only if they evaluate your input, which most of them don't. – Veedrac Jul 26 '17 at 3:26

Python 3 (CPython), Veedrac


Try it online!

Python 3, Siphor

This was fun. We need to make the type(x) != str check pass, so we need to control the return value of type(). We have to override the __class__ attribute and replace it with a custom object, that extends type, which has the __ne__ method replaced by one that always returns false. This makes it pass the type check, but the search will fail because o is not a str.

class m(type):
    def __ne__(a,b):
        return False
class c:pass

C#, TheLethalCoder

System.Nullable`1[[System.Int32, mscorlib, Version=, Culture=neutral, PublicKeyToken=b77a5c561934e089]]

Or any other nullable class.


A newline followed by a 1 works. I found it right away.


Try it online

  • Ninja'd by a minute – Cows quack Jul 24 '17 at 16:33
  • @Cowsquack The question says multiple cracks for the same cop post are allowed. – mbomb007 Jul 24 '17 at 16:40
  • I knew I should have removed newlines from the input as a first step – PunPun1000 Jul 24 '17 at 16:46

JS (ES6)

"   "

Any character with a code less than 10 should work; I've used a tab character above, which SE converts to spaces.

  • Ninja'd – programmer5000 Jul 24 '17 at 16:26
  • Sorry :( plus I think you'd need quotes around it for it to be a string – Stephen Jul 24 '17 at 16:27
  • @programmer5000, so I see :( – Shaggy Jul 24 '17 at 16:27
  • No problem, @StepHen; nature of the game. I took the quotes to be implicit, but I'll edit them in. – Shaggy Jul 24 '17 at 16:27
  • @Shaggy I dunno what the ruling is, but f(<tab>) is valid syntax (empty input) and we'd have to differentiate between f(1) and f("1") anyway – Stephen Jul 24 '17 at 16:30

JavaScript (ES6), programmer5000


Try it online!

The condition was !x||x>="\n". Any single char in an ASCII table with a code less than \n will work.

  • Yes, I thought this was it, wasn't sure... – tuskiomi Jul 24 '17 at 16:27

cQuents, Step Hen

Anything followed by a space and a positive integer. The space separates inputs, and the extra input becomes the number of the term to output.

Try it online!

  • I was just about to post a 1! You ninja'd me :/ – Mr. Xcoder Jul 24 '17 at 17:12
  • @Mr.Xcoder I typed this on mobile, hoping that nobody would ninja me :P – Pietu1998 Jul 24 '17 at 17:13

MATL, Luis Mendo (not the intended solution)

The empty input stops the program and thorws the following error:

input: reading user-input failed!

Try it online!

Node.js, Adnan

{} and {} or any 2 objects are the two inputs. I don't even understand how this works.

Here's JS's amazing object compare logics:

console.log({} == {});
console.log({} === {});
console.log({} > {});
console.log({} < {});

console.log({} >= {});
console.log({} <= {});

  • Yup, that was the intended solution :) – Adnan Jul 24 '17 at 18:04

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