How to solve Nurikabe
Wall off what is finished, shade what no island can reach, then follow the only ways out. Pools and the one-sea rule finish the job.
How it works
Nurikabe gives you a grid with some numbers. You shade cells to make the sea. The cells you leave unshaded form islands, and each island holds exactly one number: its size.
Two more rules make it a puzzle. All the sea is one piece, joined side to side. And the sea never has a pool: no 2×2 block may be all sea.
Every puzzle here has a unique solution. You never need to guess, though harder days need a short proof by contradiction.
An order that works
Start with free moves: shade around every 1 and between numbers that touch the same cell. Then mark every cell no number can reach.
After that, look for anything with one way out: an island still growing, or a piece of sea that must join the rest. Then check each 2×2 that is three quarters sea. Repeat until the grid is full.
When nothing is left, pick a cell and suppose it is sea. If that walls an island in too small or cuts the sea in two, the cell is island.
Worth memorizing
A cell between two numbers is sea.
It would join two islands.
Out of reach means sea.
Count how far each island can still grow.
No 2×2 of sea.
Three sea cells in a square make the fourth an island.
Practice
0 of 4 rightAt the start, what is the ringed cell?
What is the ringed cell?
Right after the first step, what is the ringed cell?
The 2 on the right is walled above and to the left. What is the ringed cell below it?