Nurikabe is a Japanese ( literally "invisible wall") logical game.
You plays on a grid of various dimensions (generally 6x6, 7x7, 8x8, 9x9), inside which there are some boxes with some numbers.
The objective is to individualize what boxes are black and what white are.
The black boxes represent the Walls, the whites the Gardens.
The rules are the followings:
1. Every group of white boxes "Garden" contains inside only one number;
2. The number of boxes of the Garden is equal to the number indicated inside the garden;
3. The Gardens can touch another garden only diagonally;
4. The black boxes form a Wall orthogonally continuous ;
5. Walls can not contain areas formed by 2x2 cells.

the above situation is not permitted for the points
3 - garden r5c3 and garden r6c4 are touching orthogonally
& 5 the wall contains a 2x2 area