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最新推荐文章于 2025-08-24 15:22:46 发布

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本文介绍了一种用于生成特定类型排列的算法，这类排列被称为“完美排列”。完美排列满足对于每一个位置i，其映射到的位置ppi等于i，且pi不等于i。文章通过示例代码展示了如何为给定大小n生成这样的排列，如果n为奇数，则不存在符合条件的完美排列。

A permutation is a sequence of integers p1, p2, ..., pn, consisting of n distinct positive integers, each of them doesn't exceed n. Let's denote the i-th element of permutation p as pi. We'll call number n the size of permutation p1, p2, ..., pn.

Nickolas adores （爱慕喜欢）permutations. He likes some permutations more than the others. He calls such permutations perfect. A perfect permutation is such permutation p that for any i (1 ≤ i ≤ n) (n is the permutation size) the following equations hold ppi = i and pi ≠ i. Nickolas asks you to print any perfect permutation of size n for the given n.

#include<bits/stdc++.h>
using namespace std;
int main()
{
    int n;
    cin>>n;
    if(n%2==0)
    {
        for(int i=1; i<=n; i++)
        {
            if(i==1)
                cout<<i+1;
            else if(i%2)
                cout<<" "<<i+1;
            else
                cout<<" "<<i-1;
        }
    }
    else
        cout<<-1<<endl;
    return 0;
}