codeforces 233A Perfect Permutation_codeforces seq.-优快云博客

本文链接：https://blog.youkuaiyun.com/zhang__liuchen/article/details/80042759

本文介绍了一种名为“完美排列”的特殊排列类型，并提供了一个简单的算法实现。完美排列是指在一个排列中，对于每一个位置i，其对应的元素pi不等于i且ppi等于i。文章给出了针对不同排列大小n的有效解决方案。

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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 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.

Input

A single line contains a single integer n (1 ≤ n ≤ 100) — the permutation size.

Output

If a perfect permutation of size n doesn't exist, print a single integer -1. Otherwise print n distinct integers from 1 to n, p1, p2, ..., pn — permutation p, that is perfect. Separate printed numbers by whitespaces.

   Examples
 
     input 
    
      Copy
    
1

     output 
    
      Copy
    
-1

     input 
    
      Copy
    
2

     output 
    
      Copy
    
2 1 

     input 
    
      Copy
    
4

     output 
    
      Copy
    
2 1 4 3

水题，题意不是很清楚，但是推测了一下，就过了

#include<bits/stdc++.h>  
using namespace std;  
typedef long long ll;  
const int inf = 0x3f3f3f3f;  
int main()   
{  
    // freopen("shuju.txt","r",stdin);
    int n;
    cin>>n;
    if(n&1)
        printf("-1\n");     
    else
    {
        for(int i=1;i<=n/2;i++)
        {
            if(2*i==n)
            {
                printf("%d %d\n",2*i,2*i-1);
            }
            else
                printf("%d %d ",2*i,2*i-1);
        }
    }
    return 0;  
}