How to play Hitori
A square grid of numbers with too many repeats. Shade squares until no number appears twice among the unshaded squares of any row or column.
Two more rules keep it honest: shaded squares never touch side by side, and the unshaded squares all stay joined in one piece. Every puzzle has exactly one answer, and you never need to guess it.
Rules
- Shade squares until no number repeats among the unshaded squares of any row or column.
- Shaded squares may not share a side. Touching at a corner is fine.
- The unshaded squares must form one area, joined through their sides: shaded squares may not wall any part of the grid off.
- Circles are your own notes for squares that must stay unshaded, and the game ignores them when it checks the board. The puzzle is solved the moment the shading is right.
- Shaded squares that touch, two circled squares with the same number in a line, and squares walled off from the rest turn red. Repeats underlines numbers that still clash; use it or not, your times count the same.
- A hint fixes a wrong mark, or else settles the next square that follows by logic, and keeps that solve off your best time and the leaderboard. Your puzzle stays in this browser, one per size, and the clock only runs while the page is in view.
Controls
- Click / tap a square
- Cycle: unmarked → shaded → circled → unmarked
- Right-click / long-press
- Toggle a circle
- Drag
- Circle a run of squares along a row or column
- Arrows / WASD
- Move the cursor
- Space / Enter
- Cycle the square under the cursor
- X / O
- Shade / circle
- Backspace
- Clear the square
- R
- Toggle Repeats
- H
- Hint
- Z / Ctrl+Z
- Undo
- P
- Pause
Tips
- A number between two copies of another, like 3 5 3, stays unshaded: shading the 5 would leave both 3s unshaded beside it.
- Three of a number side by side, like 4 4 4: shade both ends and keep the middle.
- Each time you shade a square, circle its neighbours; each time you circle a number, shade its copies in that row and column. Most of a solve is that chain reaction.
Hitori strategy
Start from the patterns
Three shapes get every grid going. A sandwich (2 7 2): the middle stays unshaded. A triple (5 5 5): both ends are shaded. A pair side by side (6 6): one of the two is shaded, so any other 6 in that line must be shaded too, or both of the pair would have to go and they touch. The generator keeps only puzzles where every step settles within about six squares of “if this, then that”, so a line of reasoning that runs longer is a sign to look elsewhere.
Let the chain run
One settled square spreads. A shaded square circles all its neighbours, and a circled number shades every copy of itself in its row and column, whose neighbours are circled in turn. On these puzzles a single pattern often unlocks a third of the grid, so after every new mark, follow its consequences before you hunt for the next pattern.
Guard the connection
Before you shade, check what it would wall off. A corner square’s two neighbours can never both be shaded, and neither can the three around a square on the edge. More generally, a square whose shading would close a ring or a diagonal chain of shaded squares from edge to edge must stay unshaded. The game marks walled-off squares in red, but spotting the squeeze before it happens is how fast solvers save time.
What the tools do
Repeats underlines every unshaded number that still clashes, so you can see what is left to resolve; it doesn’t touch your times. A hint first fixes a wrong mark if you have one, otherwise it settles the next square that logic gives from your correct marks, preferring one to shade. Any hint keeps the solve off your best time.
About Hitori
Hitori is one of Nikoli’s own puzzles. It first appeared in Puzzle Communication Nikoli, issue 29, in March 1990, and its full Japanese name, Hitori ni shite kure, means “leave me alone”.
Here each puzzle starts from a random Latin square, so the unshaded numbers can never clash. The generator shades squares at random until no more can be shaded without breaking a rule, gives each shaded square a number that repeats one in its row or column, and keeps the puzzle only if a solver can finish it in short steps of logic.
Questions
Can a number that appears only once in its row and column be shaded?
The rules don’t forbid it, but here it never is: every shaded square in a solution repeats a number in its row or column. A number with no copy in either can safely be circled.
Do I have to circle the unshaded squares?
No. Circles are notes. The puzzle is solved when the shaded squares are right.
Does every Hitori have one solution?
Yes. A logic solver works each puzzle out step by step before you see it, which proves the answer is unique and that it can be reached without guessing.
Which size should I start with?
The 5 × 5; the Expert level there is 1:15. The 7 × 7 comes next at 3:00, and the 9 × 9 at 6:00.
