Overview

Hitori

히토리

Shade cells so every row and column has no repeats—while keeping all unshaded cells connected.

A deceptively simple rule set that turns duplicate numbers into a satisfying chain of deductions.

Players: 1P Session length: 5-20 min

Logic PuzzleGrid Puzzle

Goal & Core Rules

Shade (blacken) some cells so that no number repeats in any row or column, shaded cells don’t touch orthogonally, and all unshaded cells stay connected.

In each row and column, each number must appear at most once among unshaded cells.
Shaded (black) cells may not be adjacent orthogonally (up/down/left/right).
All unshaded cells must form a single orthogonally connected group.
You may shade any cell, as long as all rules remain satisfied.

Controls

Mouse

Left click: toggle a cell (shade/unshade)
Right click (optional): mark as ‘maybe’/note
Hint/Undo/Restart buttons (if provided)

Keyboard

Arrow keys/Tab: move focus (if supported)
Space/Enter: toggle shade (if supported)
U: undo / R: restart (if supported)

Touch

Tap: toggle a cell (shade/unshade)
Long-press (optional): place a note mark
Hint/Undo/Restart buttons (if provided)

Beginner Tips

Start with the most duplicated numbers in a row/column—they usually produce forced shades.
Watch the ‘no-adjacent-shades’ rule: it often forces neighboring cells to stay unshaded.
Continuously check connectivity so you don’t accidentally isolate a ‘white island’.

Advanced Tips

Use connectivity proactively: if shading a cell would split the remaining whites into islands, it’s impossible.
Look for patterns where two duplicates ‘pin’ a middle segment, forcing which one must be shaded.
Work back and forth between duplicates and connectivity constraints—each unlocks the other.

Origins & History

Hitori is an original puzzle type published by the Japanese puzzle company Nikoli. It first appeared in Puzzle Communication Nikoli issue #29 in March 1990.

Timeline

1990 First published by Nikoli in Puzzle Communication Nikoli #29 (March 1990).

Notable People

Nikoli Japanese puzzle publisher credited with originating Hitori as a puzzle type

Trivia

‘Hitori’ (ひとり) literally means ‘alone’ in Japanese—reflecting the puzzle’s solitary play.

Sources

Hitori — Wikipedia

FAQ

Do diagonally touching shaded cells break the rules?

No. Only orthogonal adjacency (up/down/left/right) is forbidden for shaded cells.

What’s the most common mistake?

Forgetting the connectivity rule and accidentally leaving unshaded cells split into separate islands.

How do I get unstuck without guessing?

Re-check duplicates in the most constrained row/column and test whether a candidate shade would violate connectivity.