hot100：岛屿数量

class Solution {
public:
    vector<vector<int>> visted;
    int res = 0;

    void dfs(vector<vector<char>>& grid, int x, int y) {
        if (visted[x][y] == 0) {
            visted[x][y] = 1;
            if (grid[x][y] == '1') {
                // 遍历这个网格的四周
                if (x > 0)
                    dfs(grid, x - 1, y);
                if (y > 0)
                    dfs(grid, x, y - 1);
                if (x < grid.size() - 1)
                    dfs(grid, x + 1, y);
                if (y < grid[0].size() - 1)
                    dfs(grid, x, y + 1);
            }
        }
    }
    int numIslands(vector<vector<char>>& grid) {
        visted =
            vector<vector<int>>(grid.size(), vector<int>(grid[0].size(), 0));
        for (int i = 0; i < grid.size(); i++) {
            for (int j = 0; j < grid[0].size(); j++) {
                if (visted[i][j] == 0 && grid[i][j] == '1') {
                    res++;
                    dfs(grid, i, j);
                }
            }
        }
        return res;
    }
};