The what-if technique says: suppose a square is wall, or island, and follow what that forces. If a rule breaks, it’s the other way. It’s the technique for when nothing simpler works anywhere.
This is the last of the Nurikabe techniques. Each page shows its technique on the same 8×8 from the game, Medium level 8.
The rule
- Check that no simpler technique finds anything.
- Pick an empty square, and suppose it’s wall (or island).
- Follow what that forces with the simple techniques.
- If an island can’t be completed, or the wall makes a 2×2 block or falls into pieces, it’s the other way.
In a real puzzle
On the 8×8, it’s needed once, at step 33. Suppose row 5, column 4 is wall. Then row 5, column 5 is out of reach of every island, so it’s wall too, and with the two walls above them that makes a 2×2 block. So row 5, column 4 is island.
How often you’ll need it
Never on Easy. On 44 of the 50 Medium levels and every Hard one: 4.4 times per Medium level on average and 8 on Hard. On the 8×8 here it’s 1 of the 42 steps.