cf C. Tourist Problem

http://codeforces.com/contest/340/problem/C

#include <cstdio>
#include <cstring>
#include <algorithm>
#define maxn 100010
#define ll __int64
using namespace std;

ll a[maxn];
int n;

ll gcd(ll a,ll b)
{
    return b==0?a:gcd(b,a%b);
}

int main()
{
    scanf("%d",&n);
    ll ans=0;
    for(int i=0; i<n; i++)
    {
        scanf("%I64d",&a[i]);
        ans+=a[i];
    }
    sort(a,a+n);
    for(int i=1; i<=n-1; i++)
    {
        ans+=(a[i]-a[i-1])*i*(n-i)*2;
    }
    int k=gcd(ans,n);
    printf("%I64d %I64d
",ans/k,(ll)n/k);
    return 0;
}