bzoj2038: [2009国家集训队]小Z的袜子(hose)

#include<cstdio>
#include<iostream>
#include<cstring>
#include<algorithm>
#include<cmath>
using namespace std;
typedef long long LL;
struct node
{
    int l,r,id;
    LL fz,fm;
}a[51000];


int fk,st[51000];
bool cmp(node n1,node n2)
{
    if(st[n1.l]<st[n2.l]||(st[n1.l]==st[n2.l]&&st[n1.r]<st[n2.r]))return true;
    return false;
}
bool cmd(node n1,node n2)
{
    if(n1.id<n2.id)return true;
    return false;
}


int n,m,c[51000];LL ans,s[51000];
void update(int i,int k)
{
    ans-=s[c[i]]*s[c[i]];
    s[c[i]]+=k;
    ans+=s[c[i]]*s[c[i]];
}
LL gcd(LL a,LL b)
{
    if(a==0)return b;
    return gcd(b%a,a);
}
void solve()
{
    int l=1,r=0;ans=0;
    memset(s,0,sizeof(s));
    for(int i=1;i<=m;i++)
    {
        
        while(r<a[i].r)r++, update(r,1);
        while(r>a[i].r)update(r,-1), r--;
        while(l<a[i].l)update(l,-1), l++;
        while(l>a[i].l)l--, update(l,1);
        if(a[i].l==a[i].r){a[i].fz=0,a[i].fm=1;continue;}

        a[i].fz=ans-(a[i].r-a[i].l+1);
        a[i].fm=(LL)(a[i].r-a[i].l+1)*(LL)(a[i].r-a[i].l);
        
        LL k=gcd(a[i].fz,a[i].fm);
        a[i].fz/=k;a[i].fm/=k;
    }
}
int main()
{
    scanf("%d%d",&n,&m);
    for(int i=1;i<=n;i++)scanf("%d",&c[i]);
    for(int i=1;i<=m;i++)scanf("%d%d",&a[i].l,&a[i].r), a[i].id=i;
    
    fk=int(sqrt(n));
    for(int i=1;i<=n;i++)st[i]=(i-1)/fk+1;
    sort(a+1,a+m+1,cmp);
    
    solve();
    
    sort(a+1,a+m+1,cmd);
    for(int i=1;i<=m;i++)printf("%lld/%lld\n",a[i].fz,a[i].fm);
    return 0;
}