LeetCode Number of Islands

 1 public class Solution {
 2     public int numIslands(char[][] grid) {
 3         if(grid == null || grid.length == 0 || grid[0].length == 0){
 4             return 0;
 5         }
 6         int res = 0;
 7         for(int i = 0; i<grid.length; i++){
 8             for(int j = 0; j<grid[0].length; j++){
 9                 if(grid[i][j] == ‘1‘){
10                     res++;
11                     replace(grid,i,j);
12                 }
13             }
14         }
15         return res;
16     }
17     private void replace(char[][] grid, int i, int j){
18         if(i<0 || i>=grid.length || j<0 || j>=grid[0].length || grid[i][j] != ‘1‘){
19             return;
20         }
21         grid[i][j] = ‘0‘;
22         replace(grid,i-1,j);
23         replace(grid,i+1,j);
24         replace(grid,i,j-1);
25         replace(grid,i,j+1);
26     }
27 }