Leetcode 200 Number of Islands DFS

统计联通区域块的个数，简单dfs，请可以参考DFS框架：Leetcode 130 Surrounded Regions DFS

class Solution {
public:
    int m, n;
    bool is_in(int x, int y)
    {
        return (x < m ) && (x >= ) && (y < n ) && (y >= );
    }

    void dfs(std::vector<std::vector<char>> &board, int x, int y)
    {
        board[x][y] = '';
        int dir[][] = { { ,  }, { -,  }, { ,  }, { , - } };
        for (int i = ; i < ; ++i){
            int tx = x + dir[i][];
            int ty = y + dir[i][];
            if (is_in(tx, ty) && board[tx][ty] == '')
            {
                dfs(board, tx, ty);
            }
        }
    }

    int numIslands(std::vector<std::vector<char>>& grid)
    {
        m = grid.size();
        if (m == ) return ;
        n = grid[].size();
        if (n == ) return ;
        int ans = ;
        for (int i = ; i < m; ++i){
            for (int j = ; j < n; ++j){
                if (grid[i][j] == ''){
                    dfs(grid, i, j);
                    ans++;
                }
            }
        }
        return ans;
    }
};