Number of Islands
Given an m x n 2D binary grid grid which represents a map of '1's (land) and '0's (water), return the number of islands.
An island is surrounded by water and is formed by connecting adjacent lands horizontally or vertically. You may assume all four edges of the grid are all surrounded by water.
Example 1
1 1 1 1 0 1 1 0 1 0 1 1 0 0 0 0 0 0 0 0
Input
grid = [["1","1","1","1","0"],["1","1","0","1","0"],["1","1","0","0","0"],["0","0","0","0","0"]]Output
1All land cells are connected horizontally or vertically, forming one island.
Example 2
1 1 0 0 0 1 1 0 0 0 0 0 1 0 0 0 0 0 1 1
Input
grid = [["1","1","0","0","0"],["1","1","0","0","0"],["0","0","1","0","0"],["0","0","0","1","1"]]Output
3There are three separate groups of connected land cells, so there are three islands.
Constraints
- m == grid.length
- n == grid[i].length
- 1 <= m, n <= 300
- grid[i][j] is '0' or '1'.
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