leetcode 200 岛屿的个数

给定一个由 '1'（陆地）和 '0'（水）组成的的二维网格，计算岛屿的数量。一个岛被水包围，并且它是通过水平方向或垂直方向上相邻的陆地连接而成的。你可以假设网格的四个边均被水包围。

示例 1:

输入:
11110
11010
11000
00000
输出: 1

思路：深度优先搜索DFS

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 res = 0;
    for(int i = 0; i < m; i++){
        for(int j = 0; j < n; i++){
            if(grid[i][j] == '1'){
                dfsSearch(grid, i, j, m, n);
                res++;
            }
        }
    }
    return res;
}
public void dfsSearch(char[][] grid, int i, int j, int m, int n){
    if(i < 0 || i >= m || j < 0 || j >= n) return;
    if(grid[i][j] != '1') return;
    grid[i][j] = '0';
    dfsSearch(grid, i + 1, j, m, n);
    dfsSearch(grid, i - 1, j, m, n);
    dfsSearch(grid, i, j + 1, m, n);
    dfsSearch(grid, i, j - 1, m, n);
}