Watch the machine think

This is a real depth-first search running in your browser. Watch it place pieces, hit dead ends, and backtrack. Crank the speed to see why even millions of nodes per second are not enough for the 16×16 puzzle.

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Puzzle

Official Eternity II (16×16)

Size: 6×6

Colors: 6

Frame-restricted colors

Like the real Eternity II: confine some colors to the border band, the rest to the deep interior (needs size ≥ 4).

Seed: 1

Search path

Run

Speed: 100 steps/s

Show deepest board reached

Notice the node counter races while the depth bar barely moves? That's the whole story: on the 16×16 puzzle, no reachable speed is enough. Raw speed only divides the work by a constant; what actually moves the record is pruning the search. Why pruning beats speed →