description:

八皇后

Note:

Example:

Input: 4Output: 2Explanation: There are two distinct solutions to the 4-queens puzzle as shown below.[ [".Q..",  // Solution 1  "...Q",  "Q...",  "..Q."], ["..Q.",  // Solution 2  "Q...",  "...Q",  ".Q.."]]

answer:

class Solution {public:    int totalNQueens(int n) {        int res = 0;        vector
    
      pos(n, -1);        helper(pos, 0, res);        return res;    }    void helper(vector
     
      & pos, int row, int& res) {        int n = pos.size();        if (row == n) ++res;        for (int col = 0; col < n; ++col) {            if (isValid(pos, row, col)) {                pos[row] = col;                helper(pos, row + 1, res);                pos[row] = -1;            }        }    }    bool isValid(vector
      
       & pos, int row, int col) {        for (int i = 0; i < row; ++i) {            if (col == pos[i] || abs(row - i) == abs(col - pos[i])) {                return false;            }        }        return true;    }};
      
     
    

relative point get√：

hint :

和上面那个题一样