Hakyuu (also known as "Ripple Effect", "Hakyuu Kouka", "Hakyukoka", "Seismic") is a logic puzzle published by Nikoli. The puzzle consists of a rectangular grid of any size divided into polyomino sections called "rooms". Each room must be filled with each of the numbers from 1 to the number of cells in the room. If two identical numbers appear in the same row or column, at least that many cells with other numbers must separate them. puzzle games for adults - puzzle game for adults - puzzle game book - puzzle game adult - puzzle game brain teaser - puzzle game gift - jigsaw puzzle games - logic game book - logic game puzzles - logic games for adults - math games - math game adult - math game books - brain games - brain games for adults - brain game books - brain game puzzles - brain game adults - brain game books for seniors - brain game for adult - brain game large print