Puzzle guide
How to solve Nurikabe
Nurikabe turns a grid into a map of islands and sea. Every number is an island, and everything else is water that has to flow together. You decide cell by cell what is land and what is sea. This guide shows you the moves that do it.
The rules
- Split the grid into land and sea. Every number belongs to an island of exactly that many cells, and every island has exactly one number.
- Islands never touch left, right, up or down. Corners are fine.
- All the sea is one connected body.
- The sea never fills a whole 2×2 block.
A solved puzzle
Your first moves
- Surround every 1 with sea. A 1 is an island that is already finished.
- Find cells between two numbers. A cell that touches two islands must be sea.
- Look for sea that is about to form a 2×2 block. The fourth cell must be land.
- Mark sea on every cell no island can reach. Count how far each number can still grow.
Techniques, step by step
A finished island is fenced in by sea
When an island has as many cells as its number, it is finished, and every cell next to it is sea. A 1 is the simplest case: it is finished from the start, so its neighbours are sea before you have done anything. Later, every island you complete gives you a ring of sea the same way.
Two numbers never share an island
A cell between two numbers would join them into one island with two numbers, which is not allowed. So it is sea. The same is true when two numbers stand diagonally: the two cells that touch both of them are sea.
No 2×2 sea
Three cells of a 2×2 block are already sea. If the fourth were sea too, the sea would fill the whole block. So the fourth cell is land, and it belongs to an island that can still reach it. This is the rule that makes Nurikabe what it is, and it finds land in places the numbers seem far away from.
Only one way to grow
The 3 in the corner still needs two more cells, but the cell to its left is already sea. It has exactly one way left to grow: up. So that cell is land. Whenever an unfinished island has just one free neighbour, it must grow into it.
Cells no island can reach
A 2 can only reach the cells right next to it. Here, the cells in the middle are too far from both 2s, and no other island is near them. Nothing can ever claim them, so they are sea. On big boards, count the steps from each number: a cell that is out of reach of every island is always sea.
Every way covers the same cell
Sometimes an island can grow in a few different ways. Try them all in your head: if every one of them uses the same cell, that cell is land, whichever way the island goes. For example, a 3 that can turn left or down from the same neighbour always uses that neighbour. This is the idea that carries most medium boards.
The sea must stay in one piece
The sea in the corner is closed in by an island on one side. To join the rest of the sea, it has only one way out: down. So that cell is sea too. On harder boards, ask the opposite question as well: if this cell were land, would it cut the sea in two? If it would, the cell is sea.
Common mistakes
- Islands touching. Two islands may meet at a corner, but never side by side. If they touch, they become one island with two numbers.
- A 2×2 block of sea. It is easy to miss in a big empty area. Check every block of four when you fill in sea.
- Cutting the sea in two. The app does not mark a broken sea while you play, so check it yourself: all sea must be connected.
- An island that is too small. The app warns you about an island with too many cells, but not about one with too few. A full board with no warning can still be wrong.
Questions and answers
Ready to play?
Fence finished islands, keep numbers apart, avoid 2×2 sea and keep the sea in one piece. That is all of Nurikabe, and every board from Easy to Expert is waiting for you.