This is Nurikabe, a japanese puzzle game
To learn how to play, click here
Click a square to make it part of the continuous wall (spring green)
Click again to make it part of a group (blueviolet)
Click a third time to change it back to the default state (silver)
By default all squares silver unless part of a group
Rule 1: The squares in a group must be equal to the number shown
Rule 2: Form a continuous, non-looping wall around all groups
Rule 3: The wall can't have any groupings of 2x2 squares
More Nurikabe Puzzles:
Puzzle 1
Puzzle 2
Puzzle 3