Most broken Shikaku grids come from one of six mistakes, and the biggest is drawing a rectangle before it’s certain. The others are slips with shapes and squares: counting length instead of area, forgetting a shape, leaving a square no number can reach, taking in two numbers, and forgetting what’s already drawn. Each one is below, with how to spot it.
If you’re new, the rules and how to solve pages explain the ideas these mistakes go wrong on.
1. Drawing a rectangle before it’s certain
When a number has two shapes that might work, it’s tempting to draw one and see. A rectangle with the right area in the wrong place breaks no rule, so nothing turns red. We took every one of the game’s levels, drew one such wrong rectangle, and kept making honest moves until some number had no rectangle left that fits:
| Track | Moves before a number runs out of room (median) | Longest |
|---|---|---|
| Easy 7×7 | 2 | 14 |
| Medium 10×10 | 3 | 20 |
| Hard 12×12 | 5 | 37 |
Usually it shows up quickly, but not always. Here’s the longest wait on Easy, level 36, with the 2 in row 1, column 5 drawn sideways, where the answer has it running down:
Fourteen moves later, the 2 in row 6, column 4 has nowhere left to go, far from the mistake.
How to avoid it: only draw a rectangle when it’s the only one that fits, or a technique makes it certain.
2. Counting length instead of area
A 6 covers six squares. It can be one by six, but it can just as well be two by three, and that’s often the shape it needs.
How to avoid it: count the squares inside the rectangle, not along one side. The game’s size label (like 3×2 = 6) does it for you.
3. Forgetting a shape
A 4 can be one by four, four by one, or two by two. A 12 has six shapes. Missing one means missing the rectangle that fits.
How to avoid it: for each number, run through the ways its area divides: 12 is 1×12, 2×6, 3×4 and the same turned round.
4. Leaving a square no number can reach
Every square belongs to a rectangle. A rectangle that walls off a square, or a small pocket of squares, that no number can still reach is wrong, however good it looks.
How to avoid it: after drawing a rectangle, check the squares around it can still be reached by some number.
5. Taking in two numbers
A rectangle holds exactly one number. A big number’s rectangle often looks as if it could stretch past a small number beside it, but it can’t.
How to avoid it: check the rectangle holds only its own number before you let go.
6. Forgetting what’s already drawn
A rectangle can’t overlap one that’s already drawn. In the game, drawing over old rectangles replaces them, so a careless drag can undo good work.
How to avoid it: draw each rectangle in the empty squares only. If one vanishes, undo straight away.
How to recover from a mistake
- A red outline means a rule is broken right there: wrong area, two numbers or none.
- A number with nowhere to go means a mistake somewhere, often a long way back. Undo to the last rectangle you were sure of.
- Press Stuck? It outlines a wrong rectangle before anything else.
- Stuck with nothing wrong? List each number’s rectangles again, then look at when you get stuck.