The repeats technique says: once a number is sure to stay unshaded, every other copy of it in its row and column is shaded. No number may appear twice among a line’s unshaded squares.
This is the second of the Hitori techniques.
The rule
- Take a circled number: one you know stays unshaded.
- Look along its row and down its column for the same number.
- Shade every copy you find.
In a real puzzle
On the 9×9 every technique page follows, it’s the second move. The sandwich has just circled the 7 in row 1, column 2, and row 1 has another 7, in column 5. Shade it.
How often you’ll need it
All the time: every one of the game’s levels uses it, about 6 times on Easy, 11 on Medium and 19 on Hard. On the 9×9 here it’s 18 of the 55 moves. It’s half of the chain that solves most of every puzzle; the other half is shaded neighbours.