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).

[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). Clicking outside the grid will toggle whether black squares completely hide the numbers on them, or display them in dark grey.

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.

32.3 Singles user preferences

On platforms that support user preferences, the ‘Preferences’ option on the ‘Game’ menu will let you configure whether numbers on black squares are visible. Unlike clicking outside the grid, this will persist between games.