Hitori

Hitori first appeared in Puzzle Communication Nikoli issue 29 in March 1990. The Japanese title means something close to 'leave me alone,' which fits the goal: remove duplicate numbers until each row and column has no repeats. The twist is that shaded cells cannot touch side by side, and the remaining white cells must stay connected. That turns a simple duplicate check into a network puzzle. Start shading carefully and keep the grid in one piece.

1. Look for repeated numbers in each row and column.
2. Shade cells so no number appears more than once in any row or column.
3. Never shade two cells that touch horizontally or vertically.
4. Keep every unshaded cell connected through side contact.
5. Mark cells you know must stay white before shading around them.
6. Finish when all duplicates are resolved and the white region remains connected.

• Each row may contain only one visible copy of a number.
• Each column may contain only one visible copy of a number.
• Shaded cells may touch diagonally but not horizontally or vertically.
• All unshaded cells must form one connected group.
• Clue numbers do not change during play.
• A well-made Hitori puzzle has one logical solution.

• When three identical numbers appear in a row with the middle copy between the other two, the middle often stays white so the outer pair can be shaded.
• If shading a cell would isolate a white region, that cell must stay white.
• After you shade a cell, mark its side neighbors as white immediately.
• Search for duplicate pairs that cross. A number repeated in both a row and column can force one cell's state.
• Use connectivity late in the puzzle. A legal duplicate choice can still fail if it cuts the white area apart.

• Sudoku: Also uses rows and columns, but fills missing numbers instead of shading duplicates.
• Futoshiki: Adds inequality signs to Latin-square number placement.
• Nurikabe: Uses shaded cells and connectivity, but turns numbers into islands.

• The rules fit in a few lines.
• Every shaded cell has consequences for nearby cells.
• The connectivity rule gives the puzzle depth beyond duplicate removal.
• Small grids still produce satisfying logic chains.
• 11x11 grids create sprawling puzzles where connectivity checking becomes critical.

Play Hitori online for free and practice duplicate removal with connectivity logic. Shade slowly, mark safe cells, and recheck the white region before committing to a risky move.

Hitori rewards careful local logic and whole-grid awareness. Remove duplicates, protect white connections, and use every shaded cell to force the next decision.

• Nikoli Hitori Rules
• Hitori Puzzle Background