What's a function you've used/wrote that brought you joy?

Comments

[Edward Loveall]

If you want to create permutations, most algorithms are recursive. That means if you only want the 10,000th permutation you have to calculate the 9999 permutations before it. I was interested in calculating random-access permutations so every permutation calculation takes the same amount of time. So I wrote an algorithm and wrote up the process here.

[John Kazer]

The first time I used recursion in production code and then reused it for something slightly different. It's basically a tree traversal that gives users a sequence of different choices that depend on the previous choice.