Shikaku

Overview

Shikaku replaces a blank grid with a complete tiling of rectangles. Every rectangle must contain exactly one clue, and that clue gives its area in cells. A six could occupy a one-by-six strip, a two-by-three rectangle, or their rotations, depending on the space available. Rectangles cannot overlap and no cell may remain outside the partition. You do not fill a number sequence or place irregular pieces; the geometry is strictly rectangular. SonoTap hosts the open-source Rectangles implementation with a puzzle generator and adjustable board settings. The deceptively simple area rule becomes interesting where several clues compete for the same empty corner. Deducing which rectangle must own a hard-to-reach cell can be more useful than starting from the largest number.

How to Play

Drag from one corner of a proposed rectangle to the opposite corner to draw its outline. Include one clue and count both dimensions so their product equals that clue. A narrow rectangle still needs its full length, not merely a line joining two grid intersections. On a phone, keep the drag inside the intended starting and ending squares and use Undo to correct an inaccurate selection. Partition the entire grid into valid rectangles. Restart clears the current arrangement, while New produces another layout with the chosen settings.

Tips & Strategy

List the factor pairs of a difficult clue before testing positions. A prime area can only form a one-cell-wide strip, which sharply limits its placement near borders and other clues. Every candidate rectangle must contain its own clue and exclude every other clue. Look for empty cells reachable by only one remaining candidate, then extend that rectangle enough to cover them. Avoid committing a convenient rectangle that leaves a thin empty pocket unreachable by any clue. Near the finish, inspect the whole grid for uncovered cells rather than stopping when all numbers seem enclosed.

About this version

Shikaku uses the locally compiled rect engine from Simon Tatham’s Portable Puzzle Collection. The original authors retain credit under the MIT license. SonoTap provides the browser adaptation and this guide.