Hitori

Hitori (Japanese: "Alone" or "one person"; ひとりにしてくれ Hitori ni shite kure; literally "leave me alone") is a type of logic puzzle published by Nikoli.

Hitori is NP complete.

[1] Hitori is played with a grid of squares or cells, with each cell initially containing a number.

The game is played by eliminating squares/numbers and this is done by blacking them out.

The objective is to transform the grid to a state wherein all three following rules are true: Hitori is an original puzzle of Nikoli; it first appeared in Puzzle Communication Nikoli in issue #29 (March 1990).