Kuromasu

Kuromasu (Japanese黒 マス は どこ だKuromasu wa doko da) is a mystery, which is published by the Japanese magazine Nikoli. Kuromasu translates approximately to "Where are the black fields."

Kuromasu first appeared in Puzzle Communication Nikoli 34 (June 1991).

Regulate

Kuromasu is played on a rectangular grid of any size. Some squares are marked with numbers. Initially, all the squares are white. The goal is to find all the black squares. The following rules apply:

• Two black squares may not adjacent to each other via an edge
• All white squares form a contiguous area
• Squares with a number are always white
• The number in a square indicates the number of white fields that can be achieved horizontally and vertically from this square from without going through a black box. Where the field is counted with the number itself and all the other fields with numbers.

Normally, the solution is uniquely determined by the given numbers.

Solution strategy

To solve Kuromasu trying gradually more and more black coloring fields until finally yields the correct solution. Often it is also useful in the fields that must remain white to be marked, for example by a small black dot in the middle of the field.

Start should be a Kuromasu with particularly large or small numbers. Sometimes in a Kuromasu so incorporated large numbers, that all must ever remain aware of this number of vertical and horizontal reach fields.

Since black boxes may not adjacent to each other via edges must remain white these neighboring fields. The fact that any number field must remain white helps often to decide this case in which direction the next black box must be.