Hitori

How to play Hitori — the number shading logic puzzle

Hitori is a Japanese-style logic puzzle whose name means roughly “leave me alone” — and that is exactly the goal: work through a grid crowded with repeated numbers and shade just enough of them so that every number left standing is finally alone in its row and its column. Every square starts with a number already printed on it; nothing is blank and nothing needs to be filled in. Instead, your only decision for each cell is whether to shade it — turning it into a solid black square — or to leave it showing its number. A finished grid must satisfy three simple rules at once, and like all of our logic puzzles, every Hitori grid we generate is checked by a solving program before you ever see it, so it always has exactly one correct shading and can always be cracked by pure deduction, never a guess. This version comes in three sizes — a friendly 5×5, a tougher 7×7 and a full 8×8 challenge — each timed and scored so you can chase a spot on the leaderboard.

The goal

Shade cells until the grid obeys all three rules together: no number that is still showing (unshaded) repeats anywhere in its row or column, no two shaded squares touch edge-to-edge, and every unshaded square can still be reached from every other unshaded square by stepping only up, down, left or right. The moment all three hold at once, the puzzle is solved — there is nothing else to fill in, only cells to shade or leave alone.

The three rules

• No repeats among the unshaded cells. Look only at the numbers you have left showing — every row and every column must show each of its numbers at most once. Shaded cells don’t count at all; they are effectively removed from the grid, so shading is how you erase a duplicate.
• No two shaded cells touch. Two blacked-out squares may never share an edge — one directly above, below, or beside another is forbidden. Touching only at a corner (diagonally) is perfectly fine and very common in a finished grid.
• Every unshaded cell stays connected. All of the squares you leave showing their number must form a single, unbroken region — you can always walk from any unshaded cell to any other one by moving between orthogonally adjacent unshaded cells. Shading a cell that would wall off part of the grid is always a mistake, even if it looks like it fixes a duplicate.
• Every puzzle has exactly one solution. Before a grid reaches you, a solving program checks every possible shading and confirms only one of them satisfies all three rules — so a fully logical chain of reasoning, never a guess, is always enough to finish it.

Making moves

Tap or click any cell to shade it; tap it again to bring the number back. There is no third state to cycle through — a cell is either shaded or it isn’t. To mark a cell you are confident must stay unshaded without committing to shading anything, press and hold it for a moment (or right-click it on a desktop). A small dot appears on the cell as a personal reminder; it has no effect on the puzzle itself and can be toggled off the same way. As you play, any cell currently breaking a rule — two shaded squares touching, or two unshaded squares in the same row or column sharing a number — is outlined in red so mistakes are easy to spot and undo. A timer and mistake counter sit above the board, and you can start a fresh puzzle, jump to today’s daily puzzle, or switch grid size at any time.

Solving techniques (no guessing needed)

• Start with touching duplicates. When two identical numbers sit directly next to each other in a row or column, exactly one of the pair must be shaded — leaving both unshaded would duplicate the number, and shading both would break the no-touching rule. You won’t always know which one immediately, but marking the pair focuses your attention exactly where the puzzle needs it.
• Use the sandwich rule. Whenever the same number appears twice with exactly one cell between them — for example 5 _ 5 — that middle cell can never be shaded, no matter what number it holds. Shading it would force both matching neighbours to stay unshaded (since two shaded cells can never touch), which would leave the duplicate unresolved. So the middle cell of every such sandwich is always safe to leave alone.
• Protect connectivity. Before shading any cell, check whether doing so would trap part of the grid — for example the last unshaded cell in a corner or a dead-end row. A valid puzzle never requires you to cut off a region, so if shading a cell would isolate cells elsewhere, that cell must stay unshaded instead, even if it still has a duplicate to resolve some other way.
• Chain outward from anything you’re sure of. Once you know a cell is unshaded — because you deduced it, or because you placed a confirm mark on it — every orthogonal neighbour that shows the exact same number is forced to be shaded immediately, since two matching unshaded neighbours would duplicate each other. Following this chain out from your confirmed cells often resolves large sections of the board in one pass.

Winning and scoring

You win the instant every rule holds across the whole grid — the app checks continuously and shows a win banner as soon as your shading matches the puzzle’s one true solution. Your score rewards speed and accuracy: it starts at a base of 10,000 and loses 5 points for every second on the clock plus 200 points for every mistake, never dropping below 1. In formula terms the score is max(1, min(99999, 10000 − seconds × 5 − mistakes × 200)). A mistake is counted the instant you shade or unshade a cell to a state that disagrees with the puzzle’s unique solution — so deliberate, rule-driven play beats rapid tapping. Sign in to save your best score per size to the online leaderboard; otherwise your best result stays on your device.

Strategy tips

• Sweep the whole grid first for touching duplicate pairs and sandwich patterns — they need no context from the rest of the board and give you a strong, risk-free foothold before anything trickier comes up.
• Use the confirm-dot mark generously on cells you have proven must stay unshaded. It costs nothing, never affects scoring, and saves you from re-deriving the same deduction twice as the board fills up.
• Save connectivity reasoning for last. The no-cutting-off rule is most powerful once most of the grid is decided, since that’s when it becomes obvious which single remaining shade would wall off a region — lean on the repeat and touching rules first, then use connectivity to finish.

Frequently asked questions