What is Hitori?
Hitori starts as a grid full of numbers, with too many repeats in every row and column. You shade cells to knock the repeats out, until no number appears twice in any row or column among the cells that are left.
Two more rules keep it from being easy: shaded cells may never sit side by side, and the unshaded cells must stay joined up in one piece. Together they mean every shading choice has knock-on effects, and that is where the logic comes from.
The name is short for “Hitori ni shite kure”, Japanese for “leave me alone”. Each number left standing ends up alone in its row and column. Hitori was published by Nikoli, the Japanese puzzle company that also gave Sudoku its name.
How to start a Hitori
Scan for patterns before shading anything. A number between two copies of another number, like 3 1 3, always stays unshaded. Three copies in a row, like 2 2 2, settle all three cells: shade the ends, keep the middle.
Once a cell is shaded, circle all of its neighbors: they can’t be shaded too. Every circle then forces the other copies of that number in its row and column to be shaded, and those shadings give you more circles. Most of a solve is these two steps taking turns.
Corners and edges are worth a look early. A corner cell with one shaded neighbor needs its other neighbor unshaded, or it would be cut off from the rest of the grid.
Common mistakes
Shading one copy of a repeated number “because it has to be one of them” is the usual trap. Only shade when you can say why that copy, and not the other, must go. Otherwise circle something you’re sure of first.
The other is forgetting the connection rule until the end. Before shading a cell, check it wouldn’t wall off a pocket of unshaded cells.
Questions
- Does every Hitori have exactly one solution?
- Every Hitori on this site does. Each one is checked by a solver that follows the rules literally, so there is exactly one way to shade it and you never need to guess.
- Can shaded cells touch diagonally?
- Yes. Shaded cells can’t share a side, but touching at a corner is fine.
- What do the circles mean?
- A circle is only a note to yourself that a cell stays unshaded. It doesn’t change the answer, but circling as you go makes the next deduction much easier to see.
- How big are the puzzles?
- The daily Hitori is 7×7. Practice puzzles come in 5×5, 7×7 and 9×9.
- Is there a way to see which numbers still repeat?
- Yes. On the daily and practice boards, “Show repeats” highlights every number that still appears twice in its row or column.