The what-if technique says: suppose a square holds a star, and follow what that forces. If a rule breaks, the square is empty. It’s the technique for when nothing simpler works anywhere.
This is the last 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
- Check that no simpler technique finds anything.
- Pick a square in a crowded part of the grid, and suppose it holds a star.
- Follow what that forces with the other techniques.
- If two stars end up touching, a line or region gets too many stars, or one runs out of room, the square is empty.
In a real puzzle
On the 8×8, it’s needed once, at step 9. Suppose row 1, column 1 holds a star. Following the simpler techniques from there, 16 moves later region d has no room left for its two stars. So the square is empty.
The chain here is long; on paper you’d rarely follow one that far. In practice, try what-if on squares next to small regions, where a choice runs into trouble quickly.
How often you’ll need it
Never on the one-star tracks, and on 17 of the 50 Hard levels, 1.0 times per Hard level on average. On the 8×8 here it’s 1 of the 44 moves.