Hitori is a Japanese logic puzzle where you shade cells on a 5×5 grid so that no number repeats in any row or column, no two shaded cells share an edge, and the remaining unshaded cells form one connected area. The puzzle starts with a complete grid of numbers that intentionally contains duplicates, and your only move is to choose which cells to remove. Once you understand the three core rules — uniqueness, isolation, and connectivity — every position on the board follows from a small set of deductions. Hitori was published by Nikoli and is widely distributed as the standalone game Singles in Simon Tatham's Portable Puzzle Collection. The Hitori Puzzle tool implements these exact rules on a fixed 5×5 fixture with full keyboard controls, optional white-circle notes, immediate contradiction feedback, deterministic scoring, and a Boss Key, all running locally in your browser. This walkthrough covers what each rule means, how the controls map onto your moves, and how to read the score and the contradiction warning so the puzzle stays solvable from start to finish.
The Three Rules That Define Every Hitori Puzzle
Hitori combines three independent rules that each constrain your shading choices. Understanding them in order makes the rest of the puzzle fall into place. The table below summarizes what each rule actually limits and how to spot a violation.
| Rule | What it limits | Quick check |
|---|---|---|
| Unique numbers | Every visible number appears once per row and once per column | Count duplicates in each row and each column |
| No edge-adjacent shades | Shaded cells cannot share a horizontal or vertical edge | Inspect the immediate neighbors of every shade |
| Connected white area | Every unshaded cell must reach every other through orthogonal moves | Breadth-first traversal from any white cell |
The first rule is the one that creates most of the initial work. The fixed fixture always begins with deliberate duplicate pairs in several rows and columns, so you must decide which occurrence of each duplicate to keep and which to shade. Shaded numbers are effectively deleted, so any duplicates that remain in the white area break the rule.
The second rule is purely geometric. Two shaded cells cannot sit directly above, below, beside, or in front of one another. Diagonal contact, however, is explicitly allowed by the official Nikoli specification and the Singles documentation, and the walkthrough on diagonal contact in Hitori covers the reasoning in more depth. The only adjacency that matters is shared horizontal or vertical edges.
The third rule forces every white cell to remain reachable. After shading, you must still be able to walk from any white cell to any other using only up, down, left, and right moves without crossing a shaded cell. The interface enforces this with a breadth-first traversal that runs after every move and reports a contradiction the moment the white region splits into two islands.
These three rules together turn what looks like a simple duplicate-removal task into a compact spatial logic puzzle where every shading decision cascades into connectivity consequences.
How to Play Hitori: Keyboard Walkthrough
The Hitori Puzzle interface is built for keyboard play. Mouse and touch work as well, but every action has a single key equivalent, so you never need to take your hand off the keyboard while you reason.
- Move through the five by five grid with the arrow keys and press Space to shade or unshade a duplicate number.
- Press Enter to mark a cell as definitely white while keeping shaded cells non-adjacent and all white cells connected.
- Remove every visible row and column duplicate to finish; correct contradictions or select Restart to begin again.
The first step is the only action you will use for most cells. Arrow keys move the cursor from cell to cell. Space flips the selected cell between unshaded and shaded. There is no separate "shade once and walk away" step — every press of Space toggles the cell, so you can correct mistakes freely as new deductions appear.
The second step adds a planning tool. Enter places or removes a white-circle note on the selected cell. The note is purely a reasoning aid: it tells you that you have proved this cell must remain white. Validation ignores notes, and shading a cell automatically removes its note. Notes still count as moves, so they cost 10 points each at scoring time even though they never change the puzzle state on their own.
The third step describes what counts as finished. The browser counts visible values separately in all five rows and all five columns and flags any duplicate count above one. It checks each shaded cell's right and lower neighbors for forbidden edge adjacency. It starts at one white cell and performs a breadth-first traversal over orthogonal white neighbors. If the traversal cannot reach every white cell, the white region has split and the interface reports a contradiction. Completion requires zero duplicates, no adjacent black pair, and complete white connectivity simultaneously, all verified at the same instant.
Reading the Contradiction Warning
A contradiction message is not a permanent game over. It is a deadlock warning for your current arrangement, telling you that one or more of the three rules has just been violated. The two most common causes are two adjacent shaded cells and a sealed-off white island.
If the warning appears right after you shade a cell, look at its four edge neighbors. If any neighbor is shaded, that is the violation — the second rule has been broken. Unshade the new cell and try a different candidate, usually one further from existing shades so the connectivity rule does not get stressed in the next move.
If the warning appears without an obvious edge-adjacent pair, your move has likely boxed in a small white area. Walk the grid and try to reach every white cell from a corner using only orthogonal moves. If you find a white cell you cannot reach, your shading has split the white region. The fix is to unshade one of the cells that forms the wall around the isolated island, restoring connectivity.
The interface is built so the contradiction message stays attached to your current state until you fix it. You can keep playing other cells, but until all three rules are satisfied simultaneously, the puzzle will not register as complete and the score will not lock in.
Scoring, White Notes, and Move Count
The Hitori Puzzle tool starts every game at 1,000 points. Each move — including every shade and every note — costs 10 points, and the score cannot drop below zero. The formula is max(0, 1000 − 10 × moves), so a clean run rewards planning over exploration.
The verified solution for the fixed fixture shades five cells: the first cell, the center-right cell in row two, the final cell in row three, the second cell in row four, and the fourth cell in row five. Following that exact path uses five moves and finishes at 950 points. Notes count as moves too, so they help reasoning but lower the final score by ten each.
Because scoring is move-based, planning matters. If you are sure a cell must stay white, the efficient option is to mark it once with Enter and never touch it again, rather than repeatedly parking the cursor on it. A completed best score may be stored in browser localStorage, but nothing is uploaded or connected to an account, so scores stay private to your browser and can be wiped by clearing site data.
Restart clears shades, notes, moves, score, contradictions, and completion in one action, which makes it safe to use whenever you want to test a different approach without abandoning a session.
Controls for Mouse, Touch, and the Boss Key
Three input paths reach the same state. Keyboard users navigate with arrow keys, shade and unshade with Space, and toggle the white-circle note with Enter. Mouse and touch users can click to shade a cell, while a context-menu action toggles the white note. Every cell announces its row, column, number, and clear, shaded, or marked-white state, which keeps the interface usable with a screen reader.
The current cell has a visible site-theme outline, so you always know where the cursor is. After the puzzle is solved, input freezes until Restart so the completed state remains stable. The black and white presentation is built from CSS variables rather than canvas art, so theme switching works automatically and high-contrast modes apply cleanly.
A Boss Key is built in for shared spaces. Press Escape twice within 400 milliseconds to show the shared simulated operations spreadsheet, then repeat the double press to restore the unchanged puzzle. The cover is visual only — it does not clear any state, so the puzzle continues exactly where you left it once you toggle back.
Where Hitori Fits Among Logic Puzzles
Hitori shares the deterministic, keyboard-friendly design of several other logic games on this site. The table below compares a few options a reader might try next based on the rule shape rather than the exact arithmetic of each puzzle.
| Puzzle | Core rule | Grid size | Deterministic solution |
|---|---|---|---|
| Hitori Puzzle | Shade duplicates, isolate shades, connect whites | 5×5 | Yes — five-shade path verified |
| Nonogram | Fill cells using row and column clues | 5×5 | Yes — unique picture |
| Minesweeper | Reveal safe cells, flag hidden mines | 9×9 | Yes — fixed beginner board |
| Heyawake | One shade per room, connected whites, corridor blocks | varies | Yes |
| Numberlink | Connect matching numbers with non-overlapping paths | varies | Yes |
If you want a logic board with shading rules, connectivity constraints, and a five-move verified path, the Hitori Puzzle tool is the right starting point. For deterministic bridge-building across numbered islands, try Hashi Bridges. For deducing one unique number path through a small grid, try Hidato. For sliding tiles into order, try 15 Puzzle.
If you're weighing options, Ice Sliding Puzzle Game: 5 Fixed Rinks, 1,000 Points covers this in detail.