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# Chapter 32: Singles

You have a grid of white squares, all of which contain numbers. Your task is to colour some of the squares black (removing the number) so as to satisfy all of the following conditions:

- No number occurs more than once in any row or column.
- No black square is horizontally or vertically adjacent to any other black square.
- The remaining white squares must all form one contiguous region (connected by edges, not just touching at corners).

Credit for this puzzle goes to Nikoli [15] who call it Hitori.

Singles was contributed to this collection by James Harvey.

[15] `https://www.nikoli.co.jp/en/puzzles/hitori/`

## 32.1 Singles controls

Left-clicking on an empty square will colour it black; left-clicking again will restore the number. Right-clicking will add a circle (useful for indicating that a cell is definitely not black).

You can also use the cursor keys to move around the grid. Pressing the return or space keys will turn a square black or add a circle respectively, and pressing the key again will restore the number or remove the circle.

(All the actions described in section 2.1 are also available.)

## 32.2 Singles parameters

These parameters are available from the ‘Custom...’ option on the ‘Type’ menu.

Width, Height
  Size of grid in squares.
Difficulty
  Controls the difficulty of the generated puzzle.