how to play islands
Islands (also known as Nurikabe) is a logic puzzle on an 8x8 grid. Your job is to figure out which cells are land and which are sea.
You start with numbered island cells. The numbers tell you the size of the island. You can fill in neighboring land cells until each island reaches its target size. Mark sea around islands that are already complete.
You shouldn't need to guess. Every board has exactly one solution that can be reached by applying the rules below.
the rules
Each number counts the tiles in an island, itself included. An island can have exactly one numbered tile.
Two different islands never share an edge. Corner to corner is fine.
All sea tiles must be connected by edges, in a single unbroken stretch of water.
No four sea tiles can ever make a 2x2 block (also called a "pool").
a worked example
Let's walk through solving a 5x5 board, one step at a time. The real puzzle is 8x8, but the logic is the same.
Four islands to place: a 1, a 2, a 3 and a 4. That is 10 island tiles among 25, so the other 15 are sea.
A 1 is an island that is already finished. It needs no more land. Every tile touching it is sea.
The top-left corner is walled off from every number, so no island can reach it. Sea.
The 2 needs one more tile. If it goes left, right, or below the 2, you'd get a 2x2 pool above it, which is illegal. It must extend upwards.
That 2-sized island is complete with two tiles, so everything around it is sea.
The rest of the top row can't be a part of any island, so we can fill in the empty cells there as sea.
The 4 and the 3 have a cell between them, but it can't be land, since that would join two numbers into the same island. Mark that as sea.
The 3 can't extend to the left or above, so it must extend to the right and up. That completes the 3.
If the tile in the middle were land, it would cut off the sea below it and to its right from the rest of the sea. It must be sea.
The 4 has only one possible shape now. Any other shape would create a 2x2 pool or violate another rule above.
Fill the last tile with sea. All done!
controls
Tap a cell to mark it sea (filled: ). Tap again to mark it land (dotted: ). Tap a third time to clear it. The puzzle is solved when the sea is right, so you could also leave the land cells blank.
You can tap and drag out from a tile to fill a bunch of land or sea at once.
If using a keyboard: arrow keys move between tiles, "s" marks sea, "d" marks land, space cycles, and backspace clears a tile.
The fill sea button floods every unmarked tile with sea.
tips
- Start with the 1s. A 1 is already finished, so all four of its neighbors are sea.
- Separate two numbers with sea. A tile directly between two numbers can belong to neither island, so it is sea. When two numbers sit diagonally, the two tiles that complete the square must be sea.
- Look for three corners of a 2x2. When three tiles of a 2x2 are sea, the fourth must be land.
- Watch for sea about to be disconnected. If marking a tile as land would disconnect some water from the rest, that tile can't be land.
- Mark land as you go. It makes it easier to visualize the islands.