树和图（leetcode） ： 岛屿数量

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;
    }
};