这一题的思路是贪心，求助数学证明

#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <algorithm>
#define MAXN 100100
using namespace std;
int n,a[MAXN],b[MAXN];
int main()
{
    cin >> n;
    for (int i=1;i<=n;i++)
    	cin>>a[i];
    sort(a+1,a+n+1);
	int m=0;
    for (int i=1;i<=n/2;i++)
        b[++m] = a[i]+a[n-i+1];
    n/=2;
    sort(b+1,b+m+1);
    cout << b[n]-b[1] << endl;
    return 0;
}