Hitori
Also Known As:
Hitorinishitekure, Let Me Alone, Zahlen Streichen
Another Japanese puzzle, based on the idea of eliminating numbers according to specific rules. This puzzle appeared first in a Nikoli publication in 1990. The full name is Hitori-ni-shite-kure, 'leave me alone'.
Some of the best solving strategies are summarised, below:
If a cell has been identified as definitely white, circle the digit. Any other cells in the row or column that contain the same digit must be blacked out.
If a cell has been identified as black, the rules mean that orthogonally adjacent cells cannot be black.
If blacking out a cell would create a white island, that cell must remain white.
For any sequence of three identical adjacent digits, the centre digit must be white, because otherwise, two adjacent cells would have to be blacked out.
If there are two identical adjacent digits and another cell in the same row or column containing the same digit, the standalone digit must be black, because if it was white, the two adjacent cells would have to be blacked out.
Any digit that has two digits that are identical on either side of it must be white, because one of the two identical digits must be black – and adjacent digits cannot both be blacked out.
Instructions
All the squares contain digits. Black out certain digits in such a way that no digit appears more than once in a row or column. Blacked-out squares must not touch, either horizontally or vertically, and all remaining cells must be part of a single, unbroken area.
Related Puzzles
Bridges Futoshiki Loop-The-Loop