Hitori: rules and how to play

Goal of the game

Shade some of the printed numbers so that the remaining white cells have no duplicate number in any row or column and still form one connected area.

Rules

• Do not change or fill in numbers; decide which cells are black and which stay white.
• Among white cells, each number appears at most once per row and at most once per column. A black cell between two white duplicates does not separate that rule.
• Black cells must not share a side. They may touch diagonally.
• All white cells must connect through sides. Corner-only contact does not join them. You do not have to retain every possible number in each row.

A small example, step by step

1. Consider three consecutive cells in a row reading 4, 2, 4.
2. Both 4s cannot remain white because they repeat in the row.
3. If the middle 2 were black, both adjacent 4s would have to be white: black cells cannot share sides.
4. That would repeat 4, so the middle 2 must stay white. At least one of the 4s must be black; do not choose which without further evidence.

Beginner deductions

• A confirmed black cell forces its side-neighbours white. A confirmed white number forces all its duplicates in that row and column black.
• Use the sandwich pattern from the example, then propagate those consequences.
• Watch narrow white connections. If blackening a cell would split confirmed white cells with no alternative route, that cell must remain white.

Common mistakes

• Do not separate duplicates by a black cell and assume they no longer share a row.
• Do not let black cells touch by a side, or count diagonal white contact as connectivity.
• Do not arbitrarily choose one member of a duplicate pair before checking connectivity and neighbours.