Nurikabe – Hard

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Nurikabe, known in Japanese folklore as an invisible wall that blocks roads and causes travel delays, is a logic puzzle. It has also been named "Cell Structure" and "Islands in the Stream". The game board is a grid, typically of a rectangular shape, but without a standard size. Some cells on this grid contain numbers.

Basic Rules

1. The objective is to label each cell as either "black" or "white".
2. All black cells must be interconnected.
3. Every cell with a number must be part of a white island composed of connected white cells.
4. The size of each white island, including the cell with the number, must match the number itself.
5. Two separate white islands should not be adjacent to each other.
6. Formation of 2x2 black cell blocks is not allowed.

Additional Rules for Nurikabe

• While black cells should be connected, they can't form 2x2 squares.

Basic Solving Tips

1. Start by identifying cells that can be immediately labeled as black or white based on the given numbers.
2. Ensure no 2x2 black cells are formed.
3. Use the grid's edge to help determine which cells must be black to keep white islands separate.
4. If an island has reached its required number of white cells, ensure all its adjacent cells are black.
5. Look for "choke points" where black cells must be placed to prevent islands from connecting or getting too large.