# PuzzleShikaku

> PuzzleShikaku (https://puzzleshikaku.com) is a free website for playing and learning Shikaku, the Japanese logic puzzle also known as Rectangles, Divide by Squares or Shikaku ni Kire. Players divide a grid into rectangles so that each rectangle contains exactly one number equal to its area. Every puzzle is computer-verified to have exactly one solution.

Key facts:
- Rules: cover the whole grid with non-overlapping rectangles (squares allowed); each rectangle contains exactly one number; the number equals the rectangle's area in cells.
- Origin: invented by Yoshinao Anpuku and first published by Nikoli in 1989 (Puzzle Communication Nikoli Vol. 27).
- Japanese name: 四角に切れ (Shikaku ni Kire), "divide by squares". 四角 (shikaku) means "square / four corners".
- Complexity: deciding solvability of general Shikaku is NP-complete.
- Site features: 5x5, 7x7, 10x10, 15x15, 20x20 and 25x25 grids; Easy/Medium/Hard graded by required technique; daily (10x10), weekly (15x15) and monthly (25x25) challenges; hints, undo/redo, mistake checking, saved progress, printable sheets with answer keys, and an online Shikaku solver.

## Play
- [Shikaku Puzzle — Play Free Online (Rectangles / Divide by Squares)](https://puzzleshikaku.com/): Play Shikaku free online: divide the grid into rectangles so each one holds a single number equal to its area. 5×5 to 25×25, daily challenges, hints, printable puzzles and a solver.
- [5×5 Shikaku Puzzles — Play Free Online](https://puzzleshikaku.com/5x5-shikaku/): Play 5×5 Shikaku puzzles free online. Easy, medium and hard grids with a unique solution, hints, undo, timer and saved progress. Typical time: 1–3 minutes.
- [7×7 Shikaku Puzzles — Play Free Online](https://puzzleshikaku.com/7x7-shikaku/): Play 7×7 Shikaku puzzles free online. Easy, medium and hard grids with a unique solution, hints, undo, timer and saved progress. Typical time: 3–6 minutes.
- [10×10 Shikaku Puzzles — Play Free Online](https://puzzleshikaku.com/10x10-shikaku/): Play 10×10 Shikaku puzzles free online. Easy, medium and hard grids with a unique solution, hints, undo, timer and saved progress. Typical time: 6–15 minutes.
- [15×15 Shikaku Puzzles — Play Free Online](https://puzzleshikaku.com/15x15-shikaku/): Play 15×15 Shikaku puzzles free online. Easy, medium and hard grids with a unique solution, hints, undo, timer and saved progress. Typical time: 15–30 minutes.
- [20×20 Shikaku Puzzles — Play Free Online](https://puzzleshikaku.com/20x20-shikaku/): Play 20×20 Shikaku puzzles free online. Easy, medium and hard grids with a unique solution, hints, undo, timer and saved progress. Typical time: 25–50 minutes.
- [25×25 Shikaku Puzzles — Play Free Online](https://puzzleshikaku.com/25x25-shikaku/): Play 25×25 Shikaku puzzles free online. Easy, medium and hard grids with a unique solution, hints, undo, timer and saved progress. Typical time: 40–90 minutes.
- [Daily Shikaku — Free 10×10 Puzzle of the Day](https://puzzleshikaku.com/daily-shikaku/): A fresh 10×10 Shikaku every day — the same puzzle for every player. Solve it on consecutive days to build your streak. New puzzle every day at midnight (your local time).
- [Weekly Shikaku — Free 15×15 Challenge](https://puzzleshikaku.com/weekly-shikaku/): A hard 15×15 Shikaku that stays the same all week. Perfect for a long weekend session or a shared office challenge. New puzzle every Monday (ISO week).
- [Monthly Shikaku — Free 25×25 Challenge](https://puzzleshikaku.com/monthly-shikaku/): A giant 25×25 Shikaku marathon with dozens of rectangles. Take your time: your progress is saved automatically. New puzzle on the first day of every month.

## Learn
- [How to play Shikaku](https://puzzleshikaku.com/how-to-play/): rules, worked example, valid/invalid shapes, controls.
- [Shikaku strategy guide](https://puzzleshikaku.com/strategy/): nine solving techniques with diagrams, and how difficulty is graded.
- [History of Shikaku](https://puzzleshikaku.com/history/): Nikoli origins, names, mathematics, related puzzles.
- [Shikaku FAQ](https://puzzleshikaku.com/faq/): 20 common questions with direct answers.
- [Shikaku glossary](https://puzzleshikaku.com/glossary/): definitions of solving terms.

## Tools
- [Shikaku solver](https://puzzleshikaku.com/shikaku-solver/): enter any puzzle up to 30x30 and get the solution plus a uniqueness check.
- [Printable Shikaku](https://puzzleshikaku.com/printable/): generate printable puzzle sheets with answers.

## About
- [About and methodology](https://puzzleshikaku.com/about/): how puzzles are generated, verified unique and graded.