To solve Hitori, circle and shade in a chain. Two moves feed each other: a shaded square’s neighbours stay unshaded, and an unshaded number’s twins in its row and column are shaded. To get the chain started, look for sandwiches and pairs. When it stops, the joining-up rule takes over: any square whose shading would cut the grid in two stays unshaded. Six techniques cover every puzzle in the game.
New to Hitori? Read the Hitori rules first. This page assumes you know the three rules: no repeats among unshaded squares, no shaded squares touching, and the unshaded squares all joined up.
1. Shaded neighbours
Shaded squares can’t touch side by side, so every square beside a shaded one stays unshaded. Circle them as soon as you shade.
2. Repeats
A number left unshaded can’t appear again among the unshaded squares of its row or column, so an unshaded number’s twins in its row and column are shaded.
These first two feed each other: every square you shade circles its neighbours, and every circled number shades its twins.
3. Sandwich
A number between two of the same, like 4 2 4. If the middle were shaded, neither outer number could be (they’d touch it), so both would stay unshaded and repeat. The middle of a sandwich stays unshaded.
4. Pairs
Two of the same number side by side can’t both be shaded, so one of them stays unshaded. Any third copy of that number in the same line is shaded.
5. Cut-off
The unshaded squares must all join up. A square whose shading would wall in an unshaded square, or cut the grid in two, stays unshaded. Look for it near the edges and corners, and next to squares you’ve already shaded.
The worked example below shows one: a corner square with a shaded square below it, where shading the square beside it would wall the corner in.
6. What if
When nothing else works, pick a square and suppose it’s shaded (or unshaded). Follow what that forces with the first two techniques, and keep an eye on the joining-up rule. If a rule breaks, the square goes the other way.
It’s slower, and only needed now and then: the worked example below needs it once.
How often each technique is needed
We solved every one of the game’s 150 levels by following the hints, which always use the simplest technique that works. This is how many times each technique was used, on average, per level:
| Technique | Easy 5×5 | Medium 7×7 | Hard 9×9 |
|---|---|---|---|
| Shaded neighbours | 6.3 | 12.1 | 20.0 |
| Repeats | 5.6 | 11.3 | 18.8 |
| Sandwich | 2.0 | 2.7 | 3.5 |
| Pairs | 0.2 | 0.3 | 0.3 |
| Cut-off | 3.4 | 5.7 | 9.0 |
| What if | 0 | 0.3 | 1.9 |
The first two do most of the work. Cut-off is needed on 48 of the 50 Easy levels and every Medium and Hard one. What if is never needed on Easy, on 7 Medium levels, and on every Hard level.
A 7×7, solved in three stages
This is Medium level 44 from the game.
Stage 1: sandwiches and a pair
Five sandwiches come first, one after another, each circling a middle number. Then a pair: column 3 has two 2s side by side, in rows 5 and 6, so the 2 at its top is shaded. That starts the chain: its neighbours are circled, and one of them, the 7 in row 2, shades the other 7 in its row.
Stage 2: cut-off, then what if
Cut-off. The corner square in row 1, column 7 has a shaded square below it. Shading the square beside it, in row 1, column 6, would wall the corner in. So that square stays unshaded.
What if. Now nothing simpler works anywhere. Look at the 2 in the top-left corner, and suppose it’s shaded. Then the 1 below it stays unshaded, so the other 1 in row 2, right beside it, must be shaded. But that walls in the circled 2 in row 1, column 2: it has shaded squares on all three sides. So the corner 2 can’t be shaded. It stays unshaded.
Stage 3: the chain to the end
From there it’s the chain again: 9 repeats and 10 rounds of shaded neighbours. That leaves three squares the chain never reaches. The last three moves are cut-offs: shading any of them would cut the grid, so all three stay unshaded.
When you get stuck
- Keep the chain going. After every shade, circle its neighbours; after every circle, shade its twins.
- Look for sandwiches you’ve missed, down columns as well as along rows.
- Check the edges and corners. A shaded square near an edge often means its neighbour can’t be shaded too, or a corner would be walled in.
- Try what if on a square with few options. Suppose it’s shaded, follow the chain a few moves, and see whether anything gets walled in or repeats.
- Don’t guess. Every puzzle here can be finished by logic.