Interesting/humorous algorithms

[ible]

everything here is pretty amusing:
http://www.dangermouse.net/esoteric/

one of my favorites: dropsort is a revolutionary O(n) sorting algorithm that iterates through an array, simply dropping elements which are not sorted:
http://www.dangermouse.net/esoteric/dropsort.html

as a way to make it actually do "non-lossy" sorting, you can keep track of dropped items and recursively dropsort them, then merge with the original (undropped) list. here's a python code, for sh*ts and g*ggles.

def dropsort(A):
    len_A = len(A)
    if len_A == 0:
        return []
    A_sorted = [A[0]]
    A_dropped = []
    for i in range(1, len_A):
        if A[i] >= A_sorted[-1]:
            A_sorted.append(A[i])
        else:
            A_dropped.append(A[i])
    A_dropped = dropsort(A_dropped)
    return merge(A_sorted, A_dropped)

where the merge function is left to the reader

 

[Caine]

Obligatory xkcd 221:

int getRandomNumber()
{
   return 4; // chosen by fair dice roll.
             // guaranteed to be random.
}

 

[JDTAY]

int pyraMonthsToGo() { return pyraMonthsToGo()+2; }

ED, I think I found a bug in your code. >_>

 

[Binky]

WPEG is still my favourite. The only lossless compression algorithm where the size of the output is completely independent of the input size/complexity!

http://gkoberger.github.io/stacksort/ is good, too

 

[FBnil]

int pyraMonthsToGo() { return pyraMonthsToGo()+2; }

ED, I think I found a bug in your code. >_>

Did you find the easter egg? 2 + 2 months, quick mafs. Pyra CPU 's not hot. The ting goes speerrrahh, pap, pap.

Reversed: "pyraMonthsToGo" : Oh God, sh*t no more eep.


Algorithms in Javascript that do something:

So open a Firefox and type in the URL bar: javascript:alert(++[[]][+[]]+[+[]]);
Before hitting enter, guess what it does do....

Source: https://tutorialzine.com/2013/12/the-10-weirdest-programming-languages

 

[Caine]

That wtfjs site linked in that article is hilarious.

 

[ible]

http://gkoberger.github.io/stacksort/ is good, too

Uh… it evals both user input and random code, unchecked, from an external site. This is what security-minded folks would refer to as Very Bad™.

@Caine: regarding wtfjs, this literally was a bug in some production code i may or may not have fixed:
https://wtfjs.com/wtfs/2015-04-08-array-sort

 

[Binky]

So open a Firefox and type in the URL bar: javascript:alert(++[[]][+[]]+[+[]]);
Before hitting enter, guess what it does do....

Nothing, so far as I can tell. Does that mean I've got my browser security settings right?

 

[ible]

it says "10" in the alert box for me. you can also paste it into the chrome console, if that's something you use.

 

[JDTAY]

https://www.technologyreview.com/s/610026/algorithms-are-making-american-inequality-worse/

Algorithms are making American inequality worse... Okay, maybe not so humorous to you guys, but it sure gave Trump a good laugh when I told him about it. >_>

 

[JDTAY]

http://smbc-comics.com/comic/algorithms

 

[ible]

here's a hash-table implementation which is O(1) delete with no negative repercussions (no "deleted" flags necessary in the table), and requires no probing across the table when looking for the right key.

i call it single-probe-via-salt hash table, or salty hash table for short. each time you insert an element, a salt is prepended to the key before hashing. the salt is chosen randomly, but such that the combined salt+key hashes to an open spot in the table. so there is some initial "probing" (by modifying the salt), but subsequent calls to the table require no probing, so long as you keep the salt alongside your key.

when expanding/shrinking the table, rehashing is required, and resalting, of course. none of your previous salts will be correct anymore. you might in fact want to keep a mapping<hash-table pointer, salts> alongside your key, in case the key is used in multiple salty hash tables. for best results, you can use a salty hash table to store the salts for your keys.

 

[ible]

here's another nice and simple one:

// main.c
#include <stdio.h>
int main(int nargs, const char **vargs)
{   remove(vargs[0]);
    return 0;
}

compile with: "gcc main.c" and run with "./a.out". the second time you run it is when it does the magic.


speaking of code that deletes code, this is pretty funny:
https://github.com/munificent/vigil

Infinitely more important than mere syntax and semantics are [Vigil]'s addition of supreme moral vigilance. This is similar to contracts, but less legal and more medieval.

 

[FBnil]

@ible actually, the first time it was already gone...

 

[ible]

seriously odd, run a linux in the browser. (via javascript)
http://s-macke.github.io/jor1k/demos/main.html

create a file with the given c code above, and you can compile it and run it. totally bonkers.

 

[ible]

solving sudoku with sqlite3:
https://www.sqlite.org/lang_with.html#sudoku

 

[FBnil]

@ible wow, it took me a while to understand it.