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Nurikabe Rules: How to Play (With Examples)

Nurikabe is a logic puzzle about islands in a sea. Some squares hold numbers. You shade squares to make the wall (the sea), and leave every number an island of exactly that many squares. Shading a square says “wall”; a dot says “island”.

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The rules

Shade squares so that:

  1. Every number is in an island of exactly that many squares, joined side by side. A 3 is an island of three squares.
  2. Each island has exactly one number. Every unshaded square belongs to one of the numbered islands.
  3. The wall is one piece. All the shaded squares join up side by side.
  4. The wall has no 2×2 blocks. No four shaded squares make a square anywhere.
A solved Nurikabe A 5 by 5 grid with islands of 1, 3, 2, 2, and every other square shaded as one joined-up wall with no 2 by 2 block. 1 3 2 2
A solved 5×5: islands of 1, 3, 2 and 2, and one wall around them.

What breaks a rule

A 2×2 block of wall. Shade one more square in the grid above, in row 2, column 4, and the wall fills a 2×2 block. It also leaves that square’s island one short.

A 2 by 2 block of wall: not allowed The same grid with row 2, column 4 shaded too. That makes a 2 by 2 block of wall (ringed in red), which no Nurikabe allows, and leaves its island a square short. 1 3 2 2
One more wall square makes a 2×2 block (ringed in red): not allowed.

An island that can’t be right, with two numbers in it, more squares than its number, or closed in by wall at the wrong size. A wall in pieces, once the grid is full. In the game, a 2×2 block of wall gets a red outline, an island that can’t be right turns its number red, and a finished wall in pieces gets a red frame.

A puzzle from the game, solved

This is the first level in the game: Easy level 1, a 6×6 with seven numbers.

Easy level 1, before you start A 6 by 6 grid with 7 numbers. 1 2 2 2 2 1 2 1 2 3 4 5 6 1 2 3 4 5 6
Easy level 1, before you start.

It takes 24 steps. Here are the first three.

Steps 1 and 2: the 1s

A 1 is an island of one square, complete from the start. Every square touching it must be wall, or the island would grow. The 1 in row 1, column 3 has three squares beside it; the 1 in row 5, column 2 has four.

Easy level 1, step 1 complete-islands: wall 3 (from row 1, column 3) 1 2 2 2 2 1 2 1 2 3 4 5 6 1 2 3 4 5 6
The 1 in row 1 is complete: the squares beside it are wall.
Easy level 1, step 2 complete-islands: wall 4 (from row 5, column 2) 1 2 2 2 2 1 2 1 2 3 4 5 6 1 2 3 4 5 6
The same for the 1 in row 5.

Step 3: between two islands

Row 2, column 5 touches the 2 above it and the 2 below it. If it were island, it would join them into one island with two numbers. So it’s wall.

Easy level 1, step 3 between-islands: wall row 2, column 5 (from row 1, column 5 & row 3, column 5) 1 2 2 2 2 1 2 1 2 3 4 5 6 1 2 3 4 5 6
A square touching two different islands is wall.

The rest

From there, most of the work is finding squares no island can reach: 11 of the 24 steps. In all, it takes 4 steps from complete islands, 3 from squares between islands, 11 from squares out of reach, 5 where an island has only one way to grow, and 1 where a piece of wall has only one way out.

Easy level 1, solved Every island the right size, one wall joined up, and no 2 by 2 block. 1 2 2 2 2 1 2 1 2 3 4 5 6 1 2 3 4 5 6
Easy level 1, solved.

Where to start in any puzzle

Look for 1s: they’re complete from the start, so every square beside them is wall. Then look for squares between two numbers, which would join their islands. On the game’s levels, a 1 is the first move on 35 of the 50 Easy levels, 36 Medium and 43 Hard. A square between two islands is the first move on the rest: 13 Easy, 14 Medium and 7 Hard, apart from 2 Easy levels that start with a square out of reach.

Common mix-ups

  • Islands join side by side only. Diagonal squares don’t connect an island.
  • The wall must be one piece. Two walls that only meet at a corner aren’t joined.
  • No island without a number. Every unshaded square must belong to a numbered island.

Next steps

Questions

What does Nurikabe mean?

It’s named after a creature from Japanese folklore, an invisible wall that blocks travellers’ way. The shaded squares are the wall.

Can an island have no number?

No. Every unshaded square belongs to an island with exactly one number, and the island has exactly that many squares.

Can the wall touch the edge of the grid?

Yes. The wall can run anywhere, as long as it stays in one piece and never fills a 2×2 block.

Does every puzzle have one solution?

Yes. Every puzzle on PeerPuzzles has exactly one solution, and can be finished by logic alone, without guessing.