Number of Islands

# 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 ``` Input: grid = [ ["1","1","1","1","0"], ["1","1","0","1","0"], ["1","1","0","0","0"], ["0","0","0","0","0"] ] Output: 1 ``` ## Example 2 ``` Input: grid = [ ["1","1","0","0","0"], ["1","1","0","0","0"], ["0","0","1","0","0"], ["0","0","0","1","1"] ] Output: 3 ``` ## Constraints - `m == grid.length` - `n == grid[i].length` - `1 <= m, n <= 300` - `grid[i][j]` is `'0'` or `'1'`.