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Hitori Shaded Neighbours: Circle Around Every Shade

The shaded-neighbours technique says: every square beside a shaded one stays unshaded. Shaded squares can’t touch side by side.

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This is the third of the Hitori techniques.

The rule

  1. Shade a square.
  2. Circle the squares directly above, below, left and right of it. Corners are free.
Shaded neighbours: the squares beside a shaded one stay unshaded A 3 by 3 grid with the middle square shaded. The four squares beside it, above, below, left and right, stay unshaded. The corners are free. 1 2 3 2 3 1 3 1 2
The shaded middle square: the four squares beside it stay unshaded.

In a real puzzle

On the 9×9 every technique page follows, it’s the third move. The 7 in row 1, column 5 has just been shaded, so the squares beside it, in row 1 (columns 4 and 6) and in row 2 (column 5), stay unshaded.

Step 3: shaded neighbours Hard level 5 at step 3, with the squares this step reasons from and settles highlighted. 6 7 6 1 7 2 8 1 4 6 3 8 2 5 4 8 8 7 5 1 8 6 7 5 4 2 1 8 4 9 5 3 5 7 2 1 7 6 3 8 3 9 5 1 5 7 4 2 6 8 1 3 7 9 1 1 2 4 2 7 2 9 3 4 5 7 3 2 5 1 9 9 7 9 2 7 3 3 6 5 8 1 2 3 4 5 6 7 8 9 1 2 3 4 5 6 7 8 9
Step 3: the three squares beside the shaded 7 are circled.

How often you’ll need it

All the time: every one of the game’s levels uses it, about 6 times on Easy, 12 on Medium and 20 on Hard. On the 9×9 here it’s 22 of the 55 moves, more than any other technique. Together with repeats, it makes the chain: every shade circles its neighbours, and every circle shades its twins.

Next steps

Questions

What about squares diagonal to a shaded one?

They’re free. Shaded squares may touch at the corners; only side by side is against the rules.