51. N-Queens

八皇后想到的就是用DFS+回溯；但是实现有点麻烦，我是卡在回溯时check数组的复原情况，一开始以为只要像create_check一样简单变0就好了，最后发现会把前面设置的1给变了（有点呆
然后想到用vector直接一个temp就好了，速度有点慢，好像只比5%左右的人快，不过总归是过了

class Solution {
public:
  vector<vector<string> >res;
  vector<vector<int>>check;
  void create_check(vector<vector<int>>&check,int current_row,int col,int n){
    for(int i=0;i<n;++i){
      check[current_row][i]=1;
      check[i][col]=1;
      if(current_row+i<n&&col-i>=0)check[current_row+i][col-i]=1;
      if(current_row-i>=0&&col+i<n)check[current_row-i][col+i]=1;
      if(current_row+i<n&&col+i<n)check[current_row+i][col+i]=1;
      if(current_row-i>=0&&col-i>=0)check[current_row-i][col-i]=1;
    }
  }
    void make_queens(vector<string> &board,int current_row,int n){
      if(current_row==n){
        res.push_back(board);
        return;
      }
      for(int i=0;i<n;++i){
        if(check[current_row][i]==0){
          vector<vector<int>>temp=check;
          create_check(check,current_row,i,n);
          board[current_row][i]=\'Q\';
          make_queens(board,current_row+1,n);
          board[current_row][i]=\'.\';
          check=temp;
        }
      }
      return;
    }
    vector<vector<string> > solveNQueens(int n) {
      check=vector<vector<int>>(50,vector<int>(50,0));
        vector<string>board(n,string(n,\'.\'));
        make_queens(board,0,n);
        return res;
    }
};