Let's say you're at a store and their bathroom has a keycode. You try to guess the keycode but you notice it never tells you when you're wrong. It's likely that this keycode is a rolling code. A rolling code is one where it doesn't matter how many characters you get wrong, and once you get the right code in there it will immediately let you in.
This code makes the shortest code of a given alphabet and length that contains every subsequence of the given length of characters of the given alphabet.
Usage: node main.js alphabet length
Warning: It's very easy to run out of memory with this algorithm