标签：style blog http color 使用 io for ar div
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.."]
]
思路：使用DFS求解即可。在某行放置皇后时，检查所在列、对角线、反对角线是否已经放置了皇后。
1 class Solution { 2 public: 3 vector<vector<string>> solveNQueens( int n ) { 4 vector<string> solution( n, string( n, ‘.‘ ) ); 5 SolveSub( solution, 0, n ); 6 return solutions; 7 } 8 private: 9 void SolveSub( vector<string>& solution, int step, const int &n ) { 10 if( step == n ) { solutions.push_back( solution ); return; } 11 for( int i = 0; i < n; ++i ) { 12 bool used = false; 13 for( int k = step-1; k >= 0; --k ) { 14 if( solution[k][i] == ‘Q‘ ) { used = true; break; } 15 } 16 if( used ) { continue; } 17 for( int k = 1; k <= min( i, step ); ++k ) { 18 if( solution[step-k][i-k] == ‘Q‘ ) { used = true; break; } 19 } 20 if( used ) { continue; } 21 for( int k = 1; k <= min( n-i, step ); ++k ) { 22 if( solution[step-k][i+k] == ‘Q‘ ) { used = true; break; } 23 } 24 if( used ) { continue; } 25 solution[step][i] = ‘Q‘; 26 SolveSub( solution, step+1, n ); 27 solution[step][i] = ‘.‘; 28 } 29 return; 30 } 31 vector<vector<string>> solutions; 32 };
标签：style blog http color 使用 io for ar div
原文地址：http://www.cnblogs.com/moderate-fish/p/3938311.html
