When a number still has several rectangles, look at the squares they all share. Squares that every rectangle of a number covers are certainly that number’s, so no other number’s rectangle can use them.
This is one of the Shikaku techniques. Each page shows its technique on the same 12×12 from the game, Hard level 2.
The rule
- Pick a number that still has a few rectangles that fit.
- Find the squares every one of them covers.
- Cross out other numbers’ rectangles that use those squares.
In a real puzzle
On the 12×12, it’s first needed at step 9. The 10 in row 1, column 9 can still be several rectangles, and every one covers the squares from column 8 to column 11 of row 1. So no other number can use them, which rules out 3 rectangles of the 12 in row 2, column 7.
How often you’ll need it
On 31 of the 50 Easy levels, 48 Medium and all 50 Hard: 1.4 times per Easy level on average, 5.3 on Medium and 11 on Hard. It’s 7 of the 28 steps on the 12×12 here.