Number of islands: Tree and (leetcode)

Given consisting of  '1'(land), and  '0'(water) consisting of two-dimensional grid, the number of islands of computing. An island surrounded by water, and it is through the horizontal or vertical direction is connected to each adjacent land. You can assume that the water surrounding the four sides of the grid are.

Example 1:

Input: 
11110 
11010 
11000 
00000 

Output: 1

Example 2:

Input: 
11000 
11000 
00100 
00011 

Output: 3 

Solution (C ++):

class Solution {
public:
    //广度优先搜索
    void dfs(vector<vector<char>>& grid, int x, int y) {
        int nx = grid.size();
        int ny = grid[0].size();
        
        grid[x][y] = '0';
        if (x-1>=0  && grid[x-1][y] == '1') dfs(grid, x-1, y);
        if (x+1<nx  && grid[x+1][y] == '1') dfs(grid, x+1, y);
        if (y-1>=0  && grid[x][y-1] == '1') dfs(grid, x, y-1);
        if (y+1<ny  && grid[x][y+1] == '1') dfs(grid, x, y+1);
        
    }
    
    int numIslands(vector<vector<char>>& grid) {
        
        int island = 0;
        for (int i = 0; i < grid.size(); i++) {
            for (int j = 0; j < grid[0].size(); j++) {
                if (grid[i][j] == '1') {
                    ++island;
                    dfs(grid, i, j);
                }
            }
        }
        return island;
    }
};