B. z-sort

题目连接：

http://www.codeforces.com/contest/652/problem/B

Description

A student of z-school found a kind of sorting called z-sort. The array a with n elements are z-sorted if two conditions hold:

ai ≥ ai - 1 for all even i,
ai ≤ ai - 1 for all odd i > 1.
For example the arrays [1,2,1,2] and [1,1,1,1] are z-sorted while the array [1,2,3,4] isn’t z-sorted.

Can you make the array z-sorted?

Input

The first line contains a single integer n (1 ≤ n ≤ 1000) — the number of elements in the array a.

The second line contains n integers ai (1 ≤ ai ≤ 109) — the elements of the array a.

Output

If it’s possible to make the array a z-sorted print n space separated integers ai — the elements after z-sort. Otherwise print the only word “Impossible”.

Sample Input

4
1 2 2 1

Sample Output

1 2 1 2

Hint

题意

定义一个z排序，就是奇数位置满足ai<=a[i-1]

偶数位置满足ai>=a[i-1]

给你n个数，让你构造出来这个z排序的序列

无解输出impossible

题解：

一个小的一个大的就好了

我们先排序，然后奇数位置从1开始放，偶数位置从(n+1)/2+1开始放，这样子扔下去的奇数位置一定小于等于偶数位置。

代码

#include<bits/stdc++.h>
using namespace std;
const int maxn = 1e3+5;
int n,a[maxn],b[maxn];

int main()
{
    scanf("%d",&n);
    for(int i=1;i<=n;i++)
        scanf("%d",&a[i]);
    sort(a+1,a+1+n);
    int l=1,r=(n+1)/2+1;
    for(int i=1;i<=n;i++)
    {
        if(i%2==1)printf("%d ",a[l++]);
        else printf("%d ",a[r++]);
    }
}