leetcode【51】N-Queens
作者:互联网
问题描述:
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.
Example:
Input: 4 Output: [ [".Q..", // Solution 1 "...Q", "Q...", "..Q."], ["..Q.", // Solution 2 "Q...", "...Q", ".Q.."] ] Explanation: There exist two distinct solutions to the 4-queens puzzle as shown above.
源码:
八皇后问题。很典型的回溯法,没啥好说的。但是有两点要注意:
1.尽量弄全局变量
2.参数传递尽量中指针(即&)!参数传递尽量中指针(即&)!参数传递尽量中指针(即&)!
给大家看一下不用指针和用指针的差距
class Solution {
public:
vector<vector<string>> result;
vector<vector<string>> solveNQueens(int n) {
vector<int> visit(n, -1);
solve(0, visit);
return result;
}
void solve(int now, vector<int> &visit){
int n=visit.size();
if(now==n){
vector<string> tmp(n, string(n,'.'));
for(int i = 0; i < n; i++)
tmp[i][visit[i]] = 'Q';
result.push_back(tmp);
return;
}
for(int col=0; col<n; col++){
if(isvalid(visit, col, now)){
visit[now] = col;
solve(now+1, visit);
visit[now] = -1;
}
}
}
bool isvalid(vector<int> &visit, int col, int now){
for(int i=0; i<now; i++){
if(visit[i] == col || abs(now-i)==abs(col-visit[i]))
return false;
}
return true;
}
};
标签:...,..,int,51,visit,vector,Queens,leetcode,queens 来源: https://blog.csdn.net/fanyuwgy/article/details/104857228