Hitori is a number grid where your job is to remove repeats. You shade some cells until no number appears twice in any row or column, while keeping the shaded cells apart and the rest of the grid joined up. Every puzzle has exactly one answer.
The rules
No number may appear more than once, unshaded, in any row or column.
Shaded cells may not touch side by side. Touching at a corner is fine.
All unshaded cells must form one connected area, moving up, down, left and right.
Shading and circling
Tap a cell to shade it, tap again to circle it, and tap once more to clear it. A circle is your note that a cell definitely stays. Drag across several cells to give them all the same mark in one move.
Cells you leave unmarked count as unshaded, so you never have to circle anything. The puzzle is solved as soon as your shading follows all three rules.
Patterns to look for first
Sandwich: a number between two equal numbers, like the 3 in 5 3 5, always stays. Shading it would force both 5s to stay.
Pair: two equal numbers side by side, like 4 4, means one of them stays, so every other 4 in that row or column must be shaded.
Next to a shaded cell: every neighbor of a shaded cell stays, so circle them straight away.
Corners and edges: if shading a cell would wall off part of the grid, that cell must stay.
When you get stuck
Pick a cell and imagine shading it. If that leads straight to two touching shaded cells, a repeat you cannot remove, or a cut-off area, the cell must stay. Hard puzzles are built to need this step at least once.
Hint fixes your first wrong mark, or settles the next cell you could work out. Check outlines any wrong marks in red without revealing anything else.
Difficulty levels
Easy: a 5×5 grid that the basic rules solve.
Normal: a 7×7 grid you can solve step by step with no guessing.
Hard: a 9×9 grid that needs at least one "what if I shade this?" step.
Every puzzle is freshly made with exactly one answer, and your best time is kept for each level.