BZOJ 1679 牛的呼声

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#define maxn 10050
using namespace std;
long long n,a[maxn];
int main()
{
    scanf("%lld",&n);
    for (long long i=1;i<=n;i++)
        scanf("%lld",&a[i]);
    sort(a+1,a+n+1);
    long long ans=0;
    for (long long i=2;i<=n;i++)
        ans+=(a[i]-a[i-1])*(i-1)*(n-i+1);
    printf("%lld\n",ans*2);
    return 0;
}