What are the rules of Nurikabe?
Nurikabe is a grid with numbers in some squares. Shade squares to make the sea; the squares left unshaded are islands. Each number sits in an island of exactly that many squares, one number per island. Islands never touch side to side, the sea is all one piece, and nowhere is there a 2 × 2 block of sea.
Choose a 5 × 5, 7 × 7 or 8 × 8 grid (7 × 7 is picked to begin with); no island is larger than 5. Tap a square once to shade it, twice for a dot, your note that it is island, and again to clear it. On a keyboard, the arrows move, S shades, the full stop marks a dot and Backspace clears. A 2 × 2 of sea, or an island with two numbers or too many squares, is outlined as soon as it appears.
How do you solve Nurikabe?
- Wall in the 1s. An island of one square is finished, so every square beside it is sea.
- Separate neighbouring numbers. A square touching two different numbered islands would join them, so it is sea.
- Find squares no island can reach. If a square is too far from every number for its island to stretch there, it is sea.
- Break up pools and keep the sea joined. When three squares of a 2 × 2 are sea, the fourth is island; a piece of sea with only one way out must take it.
How is your Nurikabe time calculated?
Your result is the time from Start until the board keeps every rule; dots are only notes, and a square left unmarked counts as island. Beside the time are the times you used Check, which marks any wrong sea or dot, and Hint, which fixes a wrong mark or shades one square of sea. There is no rating, because no published typical time exists for puzzles built like these.
Does every Nurikabe here have exactly one answer?
Yes. The 90 puzzles here were made ahead of time. Islands were grown at random on an open sea, never touching and never cutting the sea apart, until no 2 × 2 pool was left, and each was given its size in one square. Most islands are 2 to 5 squares, so the numbers really have to be worked out. A puzzle was kept only if a search, trying every island shape for every number, found exactly one answer. The site's tests count every stored puzzle again and check that islands of one square stay rare.
What does Nurikabe mean?
The puzzle is named after the nurikabe, an invisible wall in Japanese folklore that blocks travellers' way, and it is published by Nikoli, the Japanese puzzle company. The shaded sea is the wall that winds between the islands. For more shading with a joined-up rule, try Hitori; for a picture revealed by counting, try Nonogram.