Your favorite algorithm!

Dear /prog/,
As I know that all of you are [b][u]EXPERT PROGRIDERS[/b][/u], I'd like to know what your personally favorite algorithms are.
I'd pick Hirschberg's algorithm, although Needleman-Wunsch is fine but requires O(mn) instead of O(min{m,n})^(Hirschberg).

So, what are your favorite algorithms?

Lol i just use high-order functions and external libraries, i don't program any algorithm other than the common if's, loops and other basic stuff those days. The most complex thing i do those days is write 2 nested loops.

That's the [code][b][i]ENTERPRISE[/i][/b][code] way. If it is too hard to solve, just download some code or buy some library.

Design a whole solution is more fun that designing algorithms, IMFO.