Number = rectangle area. Divide the grid with no gaps, no overlaps — a Japanese logic puzzle.

Shikaku (四角に切れ) is a Japanese logic puzzle in which you divide a grid into rectangles. There are only three rules — every rectangle must contain exactly one numbered cell, that number must equal the rectangle's area in cells, and every cell on the board must belong to exactly one rectangle with no gaps or overlaps. Drag your finger or mouse to draw a rectangle; tap or drag again to erase a mistake. Levels range from a quick 5×5 warm-up all the way up to a 10×10 challenge.

The winning approach is prime factoring and corner-first solving. A 1 is always a 1×1 square — place those instantly. Prime numbers like 5, 7, and 11 can only fit as 1×N or N×1 strips, narrowing their orientation enormously. Numbers next to a wall or in a corner have very few directions to grow, so they should be your second target. When two numbers sit close together, draw the boundary between their territories first to lock down candidates and accelerate the rest of the solve.

Shikaku was published in 1989 by the legendary Japanese puzzle house Nikoli — the same company that brought sudoku and slitherlink to the world. The premise is simple, but the solving process exercises area reasoning, divisor logic, and spatial visualization simultaneously, making it a quiet workout for mathematical thinking. From pencil-and-paper magazines to mobile apps, shikaku has built a devoted following and remains a fixture of Japanese newspaper puzzle pages.

FAQ — Q. Is the solution always unique? A. Yes — this game only generates puzzles with a single guaranteed solution. Q. Are there hints? A. Invalid rectangles are flagged instantly so you can re-draw. Q. Which size should I start with? A. Beginners 5×5, then 7×7 and 9×9; veterans aim for the fastest 10×10 clear.