Puzzles
Dudeney's four frogs
Two black frogs and two white frogs sit on a strip of seven lily pads, black on the left, white on the right, one empty pad in the middle. Moving one frog at a time — sliding onto an adjacent empty pad or jumping over one frog into an empty pad — swap the two colours' positions completely. What's the fewest moves?
Reveal the answer
8 moves. Henry Dudeney published this as 'The Four Frogs' in Amusements in Mathematics (1917); a related but distinct multi-piece version, 'Toads and Frogs,' was independently published by Édouard Lucas in 1883 — both belong to the same puzzle family but aren't the same puzzle.
— Henry Ernest Dudeney, Amusements in Mathematics — Thomas Nelson & Sons, 1917
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