List every way a row, column or region can hold its remaining stars without touching. A square that every way crosses out is empty; a square that’s a star in every way is a star. On two-star grids, it does much of the work.
This is one of the Star Battle techniques. Each page shows its technique on the same two-star 8×8 from the game, Hard level 34.
The rule
- Pick a row, column or region with only a few open squares.
- List every way to place its remaining stars there, none touching each other or any star already placed.
- For each way, note what it would cross out: the squares around its stars, and the line’s leftover squares.
- Cross out anything every way crosses out; place a star wherever every way has one.
In a real puzzle
On the 8×8, it’s first needed at step 5. Row 6 has five open squares, columns 4 to 8, and needs two stars, not side by side. There are six ways. In every one of them, a star touches row 7, column 5, and a star touches row 7, column 7. So both of those are empty.
How often you’ll need it
Never on the one-star tracks, and on every Hard level, 6.0 times per level on average. It’s 7 of the 44 moves on the 8×8 here.