Puzzle guide
How to solve Hitori
Hitori starts full: every cell already has a number. Your job is to black out cells until no number appears twice in any row or column. Three rules decide which ones, and a handful of patterns finds them fast.
The rules
- Black out cells so that no number appears twice, unblacked, in the same row or column.
- No two black cells may sit side by side. Touching at a corner is allowed.
- All cells left unblacked form a single connected area. None may be cut off.
A solved puzzle
Your first moves
- Look for twins side by side: two equal numbers next to each other. One of them will turn black, so any third copy in that row or column is black.
- Look for a number between two twins (like 3 1 3). It always stays.
- Every time you black out a cell, circle its four neighbours: they stay.
- Every time you circle a number, black out its copies in the same row and column.
Techniques, step by step
Twins side by side
Two 3s stand next to each other. They cannot both stay, and they cannot both be black, because two black cells may not touch. So exactly one of them stays. That means any other 3 in the same row must be black: if it stayed, there would be two 3s left.
The number between twins
Two 3s with one cell between them: at least one of them has to turn black. Whichever it is, it touches the cell in the middle. A black cell's neighbours always stay, so the 1 in the middle stays. Circle it.
Around a black cell
Two black cells may never sit side by side. So as soon as you black out a cell, all four of its neighbours stay. Circle them. This is the move you make most, and each circle you add often leads to the next black cell.
A circled number blacks out its twins
The 2 on the left is circled: it stays. A row may keep each number only once, so every other 2 in that row, and every other 2 in its column, turns black. Circles and black cells feed each other like this all through the puzzle.
Keep the white cells connected
All the cells that stay must be one connected area. The 2 in the corner has a black cell to its right, so its only way to the rest is down. If the cell below it turned black too, the 2 would be cut off. So that cell stays. On hard boards, this is the rule that decides the last cells: before you black out a cell, check that every white cell can still reach every other.
Common mistakes
- Two black cells side by side. It is the easiest rule to break. Corners touching is fine; sides touching is not.
- Cutting off a white cell. The app only checks the connection at the end, so check it yourself as you go, especially near the edges and corners.
- Blacking out too much. Only black out a cell when you know it is a repeat. A number that appears once in its row and column never needs to turn black.
- Forgetting the columns. A number can be fine in its row and still repeat in its column.
Questions and answers
Ready to play?
Twins, the number between twins, circles around black cells and white cells that stay connected: that is all of Hitori. Ready for a board?