Nurikabe

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Example of a nurikabe
Associated solution

Nurikabe ( Japanese ぬ り か べ , an invisible wall on the street, which, according to a popular myth, is responsible for the late arrival of pedestrians) is a puzzle invented by Nikoli . It was first published in Puzzle Communication Nikoli 33 (March 1991). Another name for the puzzle is Islands in the Stream .

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Nurikabe is played on a rectangular grid of any size. Some squares contain numbers. The aim of the game is to determine the color (usually black or white) for each square.

The following rules apply:

  • All black squares must be connected by edges.
  • A black square of size 2 × 2 must not appear.
  • Each number is in a white area that contains as many white squares as the number indicates.
    • In particular, the squares with the numbers are white.
  • White areas must not border one another over edges.
  • Each white area contains only one number.

Due to the alternative designation islands in the river , the white fields are often referred to as islands, the black fields as the river and black fields of the size 2 × 2 as a pond. The rules can also be formulated in this visual language, for example no “pond” may appear in the correct solution. That is why the fields are sometimes not colored black, but blue or green.

Normally the solution or the course of the current is clearly defined by the given numbers.

Solution strategy

Nurikabe animated solution.gif

To solve a Nurikabe, one typically tries first to color small fragments black, which can then be gradually connected to form larger and larger pieces.

It is often helpful to identify the fields that have to remain white, for example with a small black dot in the middle.

Since each number itself must remain white, a field with a one must not border on white fields horizontally and vertically, so these fields must be colored black. Furthermore, each white area may only contain one number and therefore a field on the edges of two numbers must be black. Even more rules can be found through logical considerations.

Web links

Commons : Nurikabe  - collection of pictures, videos and audio files