N皇后回溯解法 leetcode N-Queens

class Solution {
public:
    vector<vector<string> > solveNQueens(int n) {
    	vector<vector<string>> xxx;
        vector<vector<int> > res;
        vector<int> com;
		int len=n;
        c3(res,com,n,len,0);
        hua(xxx,res,len);
        return xxx;
    }
private:
    void c3(vector<vector<int> > &res,vector<int> &com,int n,int len,int begin)
    {
        if(len == 0 && judge(com))
        {    
			res.push_back(com);
			return ;
		}
        for(int i=0;i<n&&len>0;++i)
        {
            
            com.push_back(i);
            if(judge(com))          //剪枝，没有的话会超时
                c3(res,com,n,len-1,i);
            com.pop_back();
            
        }
    }
    bool judge(vector<int> &com)
    {
    	for(int i=0;i<com.size();i++)
    	{
    		for(int j=i+1;j<com.size();j++)
    		{
    			if(com[i] == com[j] || abs(i-j) == abs(com[i]-com[j]))
    				return false;
			}
		}
		return true;
	}
	void hua(vector<vector<string>> &str,vector<vector<int>> &com,int len)
	{
		for(auto c:com)
		{
			vector<string> ge;
			for(auto d:c)
			{
				string tem="";
				for(int i=0;i<len;++i)
				{
					if(i==d)
						tem +="Q";
					else
						tem +=".";
				}
				ge.push_back(tem);
			}
			str.push_back(ge);
		}
	}
};

　　但44ms