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==?a:gcd(b,a%b);
 }

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