Find islands in Nurikabe
Nurikabe separates numbered islands with one connected shaded sea. Count island cells carefully, then check that the surrounding sea can still connect without a solid two-by-two block.
By Zehano · Original AI-assisted explanation and worked example · Updated 16 October 2026 · Editorial approach
A worked example
A clue of 1 already occupies its island’s only cell. Every side-adjacent cell within the board must therefore be sea. Diagonal cells need separate reasoning; a corner touch does not join islands. Next consider a clue of 2 with sea above, below and to its left. If the cell to its right is available, that cell must be the island’s second cell. Once the two-cell island is complete, its other side neighbours become sea. These deductions can reveal a different constraint: if three cells in a two-by-two square are already sea, the fourth cannot also be sea. It must belong to an island, and you then need to determine which numbered island can reach it.
Try it in three steps
- Begin with completed or tightly confined islands. Include the numbered cell in the island total; a clue of 3 needs only two additional cells, not three.
- Keep island and sea connections distinct. Each island has one number and the indicated size. Different islands cannot share a side, while all sea cells must connect through side-adjacent sea cells.
- Audit the whole finished board. Count each island, confirm that every unshaded region has exactly one clue, trace the sea, and scan every two-by-two square for four shaded cells.
What to watch for
A patch of unshaded cells with no number is not a finished island. Do not leave it stranded simply because nearby clues have the correct sizes. It must connect to a suitable numbered region without merging two clues or exceeding that region’s size.
Apply it to your own material
Choose one topic from your current course or project. Write down the question you want to answer, make an attempt, and keep a note of how you checked it. Use the example above as a pattern; replace its subject matter and assumptions rather than copying an answer into a different task.
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