Puzzle & Thinking Games · 28

Sliding-block puzzles are difficult because open space is the real resource; every move spends and relocates the one gap that makes future moves possible. Puzzle difficulty is not just solution length. A short solution can be hard if the key idea is hidden, while a long solution can feel easy once the pattern is clear. Every elegant solution has an awkward ancestor made of guesses, dead ends and one unreasonable assumption.