Number of islands

• https://leetcode.com/problems/number-of-islands/

public int numIslands(char[][] grid) {
    if (grid==null || grid.length==0 || grid[0].length==0) return 0;
    int M = grid.length;
    int N = grid[0].length;

    int numLands = 0;

    for (int i = 0; i < grid.length; i++) {
        for (int j = 0; j < grid[0].length; j++) {
            if (grid[i][j] == '1') {
                numLands++;
                vistIsland(grid, i, j);
            }
        }
    }
    return numLands;
}

private void vistIsland(char[][] grid, int i, int j) {
    if (i >= 0 && j >= 0 && i < grid.length && j < grid[0].length) {
        if (grid[i][j] == '1') {
            grid[i][j] = '0';
            // visit the adjacent 
            vistIsland(grid, i + 1, j);
            vistIsland(grid, i - 1, j);
            vistIsland(grid, i, j - 1);
            vistIsland(grid, i, j + 1);
        }
    }
}