HDU 5734 Acperience

#include<cstdio>
#include<cstring>
#include<cmath>
#include<algorithm>
#include<vector>
#include<map>
#include<set>
#include<queue>
#include<stack>
#include<iostream>
using namespace std;
typedef long long LL;

const int maxn=100000+10;
int T,n;
LL w[maxn];

LL gcd(LL a,LL b) { if(b==0) return a; return gcd(b,a%b); }

int main()
{
    scanf("%d",&T);
    while(T--)
    {
        scanf("%d",&n);
        for(int i=1;i<=n;i++) scanf("%lld",&w[i]);
        LL p=0,q=0;
        for(int i=1;i<=n;i++) p=p+n*w[i]*w[i];
        LL sum=0; for(int i=1;i<=n;i++) sum=sum+abs(w[i]);
        p=p-sum*sum;
        q=(LL)n;
        if(p==0) printf("0/1\n");
        else printf("%lld/%lld\n",p/gcd(p,q),q/gcd(p,q));
    }
    return 0;
}