There's a puzzle on SumRace where the only rule is "a bigger disc can never sit on a smaller one" — and the optimal solution still takes 2ⁿ−1 moves. Tower of Hanoi. Simple rule, brutal efficiency test. sumrace.com/hanoi
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Tower of Hanoi — play free online | SumRace
Tower of Hanoi: Move the whole stack to the last peg in the fewest moves. Free, timed, with daily leaderboards.