2026-08-05 · history
Nurikabe (1991) — A Ban on Two-by-Two, Borrowed from a Yōkai's Name
In 1991, Nurikabe debuted under the pen name "renin" in the reader-development column of Puzzle Communication Nikoli #33. Its four rules — size islands by number, connect the rest into a single black sea, and never allow a two-by-two black block — weren't even expected to catch on by the magazine's own editors. In 2004 it was proven NP-complete; its "no two-by-two" rule was inherited by LITS; and in 2025, Steam's Nurikabe World brought the puzzle back under its own name. This article verifies a 34-year lineage.
