Protohackers was cool because, unlike Advent of Code, the problems seem to have less focus on "can you recognize which classic CS algorithm this is" followed by

Protohackers was cool because, unlike Advent of Code, the problems seem to have less focus on "can you recognize which classic CS algorithm this is" followed by implementating them with a gotcha. The best AOC challenges were the ones that had nothing to do with yet another Djikstras or depth first search. Protohackers is almost entirely that.