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Hitori Puzzle

Shade repeated numbers from a five by five grid while keeping black cells apart and every remaining white cell connected.

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How to use

  1. 1.Move through the five by five grid with the arrow keys and press Space to shade or unshade a duplicate number.
  2. 2.Press Enter to mark a cell as definitely white while keeping shaded cells non-adjacent and all white cells connected.
  3. 3.Remove every visible row and column duplicate to finish; correct contradictions or select Restart to begin again.

About Hitori Puzzle

Hitori Puzzle presents a five by five number grid and asks you to shade selected cells until no number repeats among the remaining white cells in any row or column. That elimination rule is only the beginning: shaded cells may not touch horizontally or vertically, and all unshaded cells must remain connected as one orthogonal region. The combination turns a simple duplicate-removal task into a compact spatial logic puzzle.

Move the selection with the arrow keys. Press Space to shade or unshade the selected cell. Press Enter to add or remove a white-circle note, which is useful when you have proved that a cell must remain visible. A white note does not change validation and cannot coexist with shading; shading automatically removes the note. Mouse and touch users can click to shade, while a context-menu action toggles the white note. After the puzzle is solved, input freezes until Restart so the completed state remains stable.

The rules follow Nikoli's official Hitori explanation and the independent Singles documentation in Simon Tatham's Portable Puzzle Collection. In each row and column, every visible number must be unique. Black cells cannot share an edge, although diagonal contact is allowed. The remaining white squares must form a single connected area through up, down, left, and right neighbors. The name and basic rule set are standard; this page's exact grid, solution fixture, score, and controls are Lizely implementation choices.

The fixed puzzle begins with deliberate duplicate pairs. Its tested solution 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. Those shades remove all row and column duplicates without adjacent black cells and leave every white cell connected. A clean five-shade solution uses five moves and finishes with 950 points from a starting score of 1,000. Notes also count as moves, so they can help reasoning but lower the final score by ten each.

Validation is recalculated after every shade. The browser counts visible values separately in all five rows and all five columns and records any count above one. It checks each shaded cell's right and lower neighbors for forbidden edge adjacency. It then 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 been split and the interface reports a contradiction. A correct result requires zero duplicates, no adjacent black pair, and complete white connectivity simultaneously.

The contradiction message is a deadlock warning for the current arrangement, not a permanent game over. You can unshade a problematic cell and continue. Automated tests cover row and column duplicates, diagonal versus orthogonal black contact, disconnected white regions, mark behavior, cursor boundaries, the disclosed five-cell solution, and a full keyboard-equivalent completion simulation. The independent fixture includes at least eight external rule golden cases rather than relying only on reversible operations.

Every cell announces its row, column, number, and clear, shaded, or marked-white state. The current cell has a visible site-theme outline. Black and white presentation uses Lizely foreground, surface, border, accent, and muted CSS variables rather than a canvas or hard-coded art palette. Gameplay is entirely local. A completed best score may be stored in browser localStorage, but nothing is uploaded or connected to an account. Restart clears shades, notes, moves, score, contradictions, and completion.

Press Escape twice within 400 milliseconds to show the shared simulated operations spreadsheet, then repeat the double press to restore the unchanged puzzle. This boss cover is visual only. Use Hitori as a short deduction break, not as a clinical test of cognition or attention. For other deterministic logic boards, try Hashi Bridges, Minesweeper, 15 Puzzle, or Maze Game.

Methodology & sources

A fixed 5×5 integer array is filtered by a Set of shaded indices. Validation counts unshaded values per row and column, checks horizontal and vertical black adjacency, and breadth-first traverses orthogonal unshaded neighbors to prove one white component. Completion requires zero duplicates, no adjacent black cells, and full white connectivity. Score is max(0, 1000 − 10×moves).

Frequently asked questions

What is the goal in Hitori?
Shade cells until each visible number is unique within its row and column, with no adjacent black cells and one connected white area.
Can black cells touch diagonally?
Yes. Diagonal contact is allowed; only horizontal and vertical edge-sharing between black cells is forbidden.
What does the white circle mean?
It is an optional reasoning note that marks a cell you intend to keep white. It does not change the puzzle rules.
Why does the game report a contradiction?
The current shades either put black cells side by side or split the remaining white cells into disconnected regions.

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