Nurikabe (puzzle)

Nurikabe (Japaneseぬりかべ, an invisible wall on the street, which is responsible for a popular myth for the lateness of pedestrians ) is a puzzle that was invented by Nikoli. It first appeared in the journal Puzzle Communication Nikoli 33 ( March 1991). Another name for the puzzle is Islands in the Stream.

Regulate

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

The following rules apply:

• All black squares must be related to each other via edges.
• A black square of size 2 × 2 may not occur.
• Each number is in a white area, which contains as many white squares as the number indicates. In particular, the squares are white with the numbers.

Due to the alternative designation Islands in the Stream, the white boxes are often referred to as islands, the black squares as electricity and black squares of size 2 × 2 as a pond. The rules can also be formulated in this imagery, we may then, for example, no " pond " occur in the correct solution. Therefore, sometimes the fields are not black but blue or green colored.

Normally, the solution or the course of the current is uniquely determined by the given numbers.

Solution strategy

To solve Nurikabe trying typically first small fragments of black coloring, which can then be gradually connect to increasingly larger sections.

Often it is helpful to the fields that need to remain white, to be marked, for example by a small black dot in the middle.

Since each number itself must remain white, a field with a one may laterally and vertically adjacent to white squares, so that these fields must be black in color. Furthermore, any white area may only contain a number and must therefore two numbers a field at the edge adjacent black. By logical reasoning can be so find some more rules.