Every square belongs to some rectangle. A square that only one number’s rectangles can reach must be in that number’s rectangle, so its rectangles that miss the square are out.
This is the last of the Shikaku techniques. Each page shows its technique on the same 12×12 from the game, Hard level 2.
The rule
- Pick a square that isn’t in a rectangle yet.
- Ask which numbers could still have a rectangle covering it.
- If only one can, cross out that number’s rectangles that miss the square.
In a real puzzle
On the 12×12, it’s needed once, at step 17. Only the 12 in row 2, column 7 can still reach row 2, column 2. So the 12’s rectangle must cover it, which rules out 2 of the 12’s rectangles.
How often you’ll need it
Never on Easy, on 9 of the 50 Medium levels and every Hard one: 0.9 times per Medium level on average and 5.7 on Hard. It’s 1 of the 28 steps on the 12×12 here.