第一个题解！

#include<bits/stdc++.h>
#define fi first
#define se second 
#define pa pair<int,int>
#define int long long
using namespace std;
const int N=1e5+5;
int a[N],c[N],sm,ans[N],ans2[N];
int clac(int x){
	return x*(x-1)/2;
}
void add(int x){
	c[a[x]]++;
	int t=c[a[x]];
	sm=sm-clac(t-1)+clac(t);
}
void del(int x){
	c[a[x]]--;
	int t=c[a[x]];
	sm=sm-clac(t+1)+clac(t);
}
int gcd(int a,int b){
	if (b==0) return a;
	if (a<b) return gcd(b,a);
	return gcd(b,a%b);
}
signed main(){
	ios::sync_with_stdio(0);
	cin.tie(0),cout.tie(0);
	int n,m;
	cin >> n >> m;
	int L=sqrt(n);
	for (int i=1;i<=n;++i) cin >> a[i];
	vector<pair<int,pa>> que;
	int l,r,lp,rp;
	for (int i=1;i<=m;++i){
		cin >> l >> r;
		pa t;t.fi=l,t.se=r;
		que.emplace_back(i,t);
		ans2[i]=clac(r-l+1);
    }
	sort(que.begin(),que.end(),[&L](const pair<int,pa> &a1,const pair<int,pa> &b1){
		pa a=a1.se,b=b1.se;
		if (a.fi/L==b.fi/L) return a.se<b.se;
		return a.fi<b.fi; 
	});
	l=r=1,add(1);
	for (auto &q:que){
		lp=q.se.fi,rp=q.se.se;
		for (int i=l-1;i>=lp;--i) add(i);
		for (int i=l;i<lp;++i) del(i);
		for (int i=r;i>rp;--i) del(i);
		for (int i=r+1;i<=rp;++i) add(i);
		ans[q.fi]=sm;
		l=lp,r=rp;
	}
	for (int i=1;i<=m;++i){
		int t=gcd(ans[i],ans2[i]);
		if (ans[i]==0) t=1,ans2[i]=1;
		cout<<ans[i]/t<<"/"<<ans2[i]/t<<"\n";
	}
	cout.flush();
	return 0;
}