LeetCode 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.."]]

经典皇后问题，递归回溯搜索。

vector<vector<string> >  res;bool CanPut(vector<string>& tmp, int row, int col, int n){int i=0, j=0;//row行，col列有'Q'返回falsefor(i=0; i<row; i++){if(tmp[i][col] == 'Q')return false;}//row行，col列的左斜对角有'Q'返回falsefor(i=row-1, j=col-1; i>=0 && j>=0; i--, j--){if(tmp[i][j] == 'Q')return false;}//row行，col列的右斜对角有'Q'返回falsefor(i=row-1, j=col+1; i>=0 && j<n; i--, j++){if(tmp[i][j] == 'Q')return false;}return true;}void solve(vector<string>& tmp, int row, int n){if(row==n){res.push_back(tmp);return ;}for(int col=0; col<n; col++){string s(n, '.');if(CanPut(tmp, row, col, n)){//如果在row行，col列可以放‘S’s[col] = 'Q';tmp.push_back(s);solve(tmp, row+1, n);//回溯，递归中很重要的一步//如果不满足，则回退一步搜索tmp.pop_back();}}}vector<vector<string> > solveNQueens(int n){if(n == 0)return res;vector<string> tmp;solve(tmp, 0, n);return res;}