by Ted Warner (Author)

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.