A while ago a friend sent me a simple puzzle: write a program that enumerates all sets of nested parenthesis. I started with an intractable, naive solution and after some discussion and a dead end or two I wound up with a decent dynamic programming solution.
In Knuth’s The Art of Computer Programming: volume 4 section 220.127.116.11 he describes Algorithm P, which is much more clever than the one I came up with. It prints the nested parentheses in lexicographic order. I implemented it in Python and figured I would post it for folks put off by Knuth’s notation.