It's an evolutionary algorithm! A silly one, but it gets the point across. The point of the search is to recover the input string. It does this by creating a "population" of random parent strings. Then it "mutates" and "crosses" the parents to create a new population, and then selects the most fit strings to use as the parents. (Fitness is defined as how many characters of the string they have in common). This process continues until the fittest string is the same as the search string.
You can build it by running make (it should build on Linux with no fuss). Run
it with bin/release/evolve [string-to-search-for]. It'll output the fitness
of each generation's top individual as it goes. It may take a long time for
long strings (or segfault if you make the string big enough).
The idea for this code isn't original -- I saw the idea mentioned on StackOverflow, and apparently the SO user got the idea for it from something called Rosetta Code. It's a fun coding exercise for me.