莫队算法

#include<cstdio>
#include<cmath>
#include<algorithm>
using namespace std;

  long long  lm,rm;
  long long c[50001],a[50001];
  long long t1,t2;
  long long ans;
  
  struct data{
      long long  l,r,key1,num;
  }q[50001];
  
  struct str{
      long long s,m;
  }an[50001];

  bool comp(const data &a, const data &b){
      if (a.key1<b.key1) return(1);
      if (a.key1>b.key1) return(0);
      if (a.r<b.r) return(1);
      return(0);
  }
  
  long long gcd(long long a,long long b){
      if (a%b==0) return(b);else return(gcd(b,a%b));
  }
  
  void movel(long long targ){
      if (lm<targ)
        for (;lm<targ;){
          ans=ans-c[a[lm]]*(c[a[lm]]-1)+(c[a[lm]]-1)*(c[a[lm]]-2);
          c[a[lm]]--;
          lm++;
          }
        
    if (lm>targ)
      for (;lm>targ;){
          lm--;
          ans=ans-c[a[lm]]*(c[a[lm]]-1)+c[a[lm]]*(c[a[lm]]+1);
          c[a[lm]]++;
      }  
  }
  
  void mover(long long  targ){
      if (rm<targ)
      for (;rm<targ;){
          rm++;
          ans=ans-c[a[rm]]*(c[a[rm]]-1)+(c[a[rm]]+1)*c[a[rm]];
          c[a[rm]]++;
      }
      
    if (rm>targ)
    for (;rm>targ;){
        ans=ans-c[a[rm]]*(c[a[rm]]-1)+(c[a[rm]]-1)*(c[a[rm]]-2);
        c[a[rm]]--;
        rm--;
    }  
  }
  
  int main(){
       
    long long n,m;
    scanf("%lld%lld",&n,&m);
    int siz=int(sqrt(n));
    
    for (long long i=1;i<=n;i++) scanf("%lld",&a[i]);
    for (long long i=1;i<=m;i++) {
        scanf("%lld%lld",&q[i].l,&q[i].r);
        q[i].key1=q[i].l/siz;
        q[i].num=i;
    }      
    
    sort(q+1,q+m+1,comp);
    
    lm=1,rm=0;
    ans=0;    
     for (long long i=1;i<=m;i++){
        movel(q[i].l);mover(q[i].r);
        t1=ans;t2=(rm-lm+1)*(rm-lm);
        if (t1!=0){
        long long gc=gcd(t1,t2);
        an[q[i].num].s=t1/gc;an[q[i].num].m=t2/gc;
        } else {
            an[q[i].num].s=0;an[q[i].num].m=1;
        }
    }
    
    for (int i=1;i<=m;i++) printf("%lld/%lld\n",an[i].s,an[i].m);
  }