Each island can only grow as far as its number allows, and never right next to another island. A square that no island can reach is wall. It does more work than any other technique in Nurikabe.
This is one of the Nurikabe techniques. Each page shows its technique on the same 8×8 from the game, Medium level 8.
The rule
- For each island, count how many squares it still needs.
- Mark every square it could reach in that many steps, going through empty squares and never touching another island.
- Any empty square no island can reach is wall.
In a real puzzle
On the 8×8, it’s first needed at step 7. Row 1, column 5 is too far from every number to be part of any island, so it’s wall.
How often you’ll need it
On every one of the game’s 150 levels, more than any other technique: 10.6 times per Easy level on average, 15.8 on Medium and 22.6 on Hard. It’s 15 of the 42 steps on the 8×8 here.