[LeetCode] N-Queens

最新推荐文章于 2021-02-28 00:03:49 发布

zjjee

最新推荐文章于 2021-02-28 00:03:49 发布

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本文详细介绍了如何使用回溯算法解决n皇后问题，并通过C++代码实例展示了解决方案。

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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.."]
]

class Solution {
public:
    vector<vector<string> > ans;
    vector<string> v;
    int *col;
    string s;
    vector<vector<string> > solveNQueens(int n) {
        for(int i = 0;i < n;i ++)
            s.push_back('.');
        col = new int[n];
        generate(n,0);
        return ans;
    }
    void generate(int n,int dep){
        if(dep == n){
            ans.push_back(v);
            return;
        }
        for(int i = 0;i < n;i ++){
            if(check(dep,i)){
                string ss = s;
                ss[i] = 'Q';
                v.push_back(ss);
                generate(n,dep + 1);
                v.pop_back();
                col[dep] = -1;
            }

        }
    }
    bool check(int k,int i){
        col[k] = i;
        for(int i = 0;i < k;i ++)
            if(col[i] == col[k] || abs(col[i] - col[k]) == abs(i - k)) return false;
        return true;
    }
};