Hitori
Officially Hitori (ひとりにしてくれ)
NIKOLI-PUBLISHED JAPANESE LOGIC PUZZLE from 1990 — solve a grid of NUMBERS by SHADING (BLACKING OUT) selected cells such that: (1) NO SHADED CELLS TOUCH ORTHOGONALLY, (2) UNSHADED CELLS FORM ONE CONNECTED REGION, (3) NO ROW OR COLUMN CONTAINS A REPEATED NUMBER in UNSHADED cells. Elegant + minimalist. Popular in Nikoli's puzzle magazines + at WORLD PUZZLE CHAMPIONSHIP grid rounds.
Quick facts
Category
Puzzle Games
Type
Individual
Players
1–1
Duration
~15 min
Where played
indoor
Country of origin
🇯🇵 Japan
Estimated origin
Invented + first published 1990 in Nikoli's Puzzle Communication magazine, Japan; adopted by international puzzle community + World Puzzle Championship rounds early 2000s.
Olympic
No
Popularity
regional
How it works
Objective
Shade cells satisfying 3 rules simultaneously: no two shaded cells adjacent, unshaded remain connected, no repeated digits in row/column among unshaded.
Rules
Basic rules
SHADED CELLS: no two shaded cells share an EDGE (horizontal or vertical)
Signature no-adjacent-shaded rule.
UNSHADED CELLS: must form a SINGLE ORTHOGONALLY CONNECTED REGION (no isolated islands)
Signature connected-unshaded rule.
UNSHADED CELLS: no digit appears MORE THAN ONCE per row OR per column
Signature no-repeat digit rule.
PUZZLE has UNIQUE SOLUTION — pure logic (no guessing needed for well-set puzzles)
Signature unique-solution rule.
COMMON TECHNIQUES: (1) TWO SAME DIGITS IN ROW/COL — if enclosing a middle-third same digit, middles must be UNSHADED; (2) NO ORTHOGONAL PAIR: adjacent same digits = one MUST shade one; (3) CONNECTIVITY constraint — cells linking must stay unshaded
Signature solve techniques.
Scoring
Correctness only; timed in competition (fastest correct solve = winner).
Win condition · Correctly-shaded grid; in WPC, fastest correct time.
Equipment
PUZZLE GRID: typically 5×5 to 12×12 filled with digits 1 to N (numbers repeat in rows + columns)
Signature filled digit grid.
PENCIL + ERASER (traditional) or DIGITAL app / stylus
Standard writing tools.
SHADING (dot / X / darken) for cells being blacked out
Signature shading marks.
Terminology
- Nikoli
- Japanese puzzle publisher (Tokyo, since 1980) originating this + many Nikoli-standard puzzles.
- Shading
- Blacking-out cells to satisfy constraints.
- Connected region
- All unshaded cells form one orthogonally-linked group.
- No-touch rule
- Shaded cells cannot be orthogonally adjacent.
- Ittai
- Japanese for 'as one' — referring to unshaded connectivity requirement.
Major competitions
World Puzzle Championship (WPC — Hitori commonly featured)
annual · Global (rotating host) · since 1992
US Puzzle Championship
annual · USA · since 2000
Where it is played
Governing bodies
Nikoli (originator / publisher)
Founded 1980 · Tokyo, Japan
World Puzzle Federation (WPF)
Founded 1999 · Global
Famous names & records
Famous athletes
- Ulrich Voigt (DE, WPC champion)
- Thomas Snyder (US, WPC champion)
- Jakub Hrazdira (CZ)
- Roland Voigt (DE, WPC top solver)
Sources & provenance
- Wikipedia — Hitori— Wikipedia
- Nikoli — Hitori— Nikoli