n-queens

The n-queens puzzle is the problem of placing n queens on an n×n chessboard such that no two queens attack each other.

Given an integer n, return all distinct solutions to the n-queens puzzle.
Each solution contains a distinct board configuration of the n-queens’ placement, where’Q’and’.’both indicate a queen and an empty space respectively.
For example,
There exist two distinct solutions to the 4-queens puzzle:
[
[“.Q..”, // Solution 1
“…Q”,
“Q…”,
“..Q.”],

[“..Q.”, // Solution 2
“Q…”,
“…Q”,
“.Q..”]
]

class Solution {
public:
    bool judge_quee(string &vec)  //判断n个皇后是否在对角线上
        {
        int len=vec.size();
        if(len<=1)
            return true;
        for(int i=0;i<len;++i)
            for(int j=i+1;j<len;++j)
            {
            if(i-j==vec[i]-vec[j]||j-i==vec[i]-vec[j])
                return false;
        }
        return true;
    }
    vector<vector<string> > solveNQueens(int n) {
        string vec;
        for(int i=0;i<n;++i)
            vec+=(i+'0');
        vector<vector<string> > res;
        recur_pai(res,vec,0);
        return res;        
    }
    void recur_pai(vector<vector<string>> &res,string &vec,int begin)//求全排列
        {
        if(begin==vec.size()&&judge_quee(vec)){
           vector<string> temp(vec.size(),string(vec.size(),'.'));
           for(int i=0;i<vec.size();++i)
               {
               temp[i][vec[i]-'0']='Q';
           }
           res.push_back(temp);
        }
        for(int i=begin;i<vec.size();++i){
            swap(vec[begin],vec[i]);
            recur_pai(res,vec,begin+1);
            swap(vec[begin],vec[i]);
        }
    }
};