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//200
//11110
//11010
//11000
//00000
//1
//200-Solution1
void bfs(int i, int j, int n, int m, vector<vector<char>>& grid) {
    if (i<0 || i>n-1 || j<0 || j>m-1 || grid[i][j]=='0')
        //[0~n-1],递归边界是出界或者找到为0的值
        return;
    grid[i][j]='0';//搜索到为1的值置0，不用再次遍历
    bfs(i-1, j, n, m, grid);
    bfs(i+1, j, n, m, grid);
    bfs(i, j-1, n, m, grid);
    bfs(i, j+1, n, m, grid);//上下左右，可以换顺序
}
int numIslands0(vector<vector<char>>& grid) {
    if (grid.empty()) {
        return 0;
    }
    int n = grid.size();
    int m = grid[0].size();
    int res = 0;
    for (int i = 0; i < n; ++i) {
        for (int j = 0; j < m; ++j) {
            if (grid[i][j] == '1') {
                bfs(i, j, n, m, grid);
                res++;
            }
        }
    }
    return res;
}

//200-Solution2
void dfs(int i, int j, int n, int m, vector<vector<char>>& grid) {
    grid[i][j] = 0;
    if (i>0 && grid[i-1][j] == '1') {
        dfs(i-1, j, n, m, grid);
    }
    if (i<n-1 && grid[i+1][j] == '1') {
        dfs(i+1, j, n, m, grid);
    }
    if (j>0 && grid[i][j-1] == '1') {
        dfs(i, j-1, n, m, grid);
    }
    if (j<m-1 && grid[i][j+1] == '1') {
        dfs(i, j+1, n, m, grid);
    }
}
int numIslands(vector<vector<char>>& grid) {
    if (grid.empty()) {
        return 0;
    }
    int n = grid.size();
    int m = grid[0].size();
    int res = 0;
    for (int i = 0; i < n; ++i) {
        for (int j = 0; j < m; ++j) {
            if (grid[i][j] == '1') {
                dfs(i, j, n, m, grid);
                res++;
            }
        }
    }
    return res;
}