NumberOfIslands.java

package matrix;
// Source : https://leetcode.com/problems/number-of-islands/
// Id     : 200
// Author : Fanlu Hai | https://github.com/Fanlu91/FanluLeetcode
// Date   : 2021/2/20
// Topic  : dfs
// Level  : Medium
// Other  :
// Tips   :
// Links  : Must
// Result : 91.40% 15.30%

public class NumberOfIslands {
    // 91.40% 2ms 15.30%
    public int numIslands(char[][] grid) {
        int count = 0;
        for (int i = 0; i < grid.length; i++) {
            for (int j = 0; j < grid[0].length; j++) {
                if (grid[i][j] == '1') {
                    dfs(grid, i, j);
                    count++;
                }
            }
        }
        return count;
    }

    private void dfs(char[][] grid, int i, int j) {
        if (i < 0 || j < 0 || i >= grid.length || j >= grid[0].length || grid[i][j] == '0')
            return;
        grid[i][j] = '0';
        dfs(grid, i + 1, j);
        dfs(grid, i, j + 1);
        dfs(grid, i - 1, j);
        dfs(grid, i, j - 1);
    }
}