Number of Islands
Medium
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.
Constraints
- m == grid.length
- n == grid[i].length
- 1 <= m, n <= 300
- grid[i][j] is '0' or '1'
Example
Sample Input:
grid = [ ["1","1","1","1","0"], ["1","1","0","1","0"], ["1","1","0","0","0"], ["0","0","0","0","0"] ]
Expected Output: 1
Edge Cases
- An empty grid. The result should be 0.
- A grid containing only water ('0's). The result is 0.
- A grid containing only land ('1's). The result is 1.
- Islands that touch at the corners but not edges are considered separate.