小Z的袜子(题解)(莫队)

题目

code

#include<bits/stdc++.h>
#define lst long long
#define ldb double
#define N 50050
using namespace std;
const int Inf=1e9;
int read()
{
    int s=0,m=0;char ch=getchar();
    while(ch<'0'||ch>'9'){if(ch=='-')m=1;ch=getchar();}
    while(ch>='0'&&ch<='9')s=(s<<3)+(s<<1)+(ch^48),ch=getchar();
    return m?-s:s;
}

int n,m,unit;lst Ans;
int col[N],bl[N];lst sum[N];
struct Ques{lst A,B;int le,ri,id;}ljl[N];
bool cmp_Q (Ques a,Ques b){return bl[a.le]==bl[b.le]?a.ri<b.ri:a.le<b.le;}
bool cmp_id(Ques a,Ques b){return a.id<b.id;}
void Update(int now,int xx)
{
    Ans-=sum[col[now]]*sum[col[now]];
    sum[col[now]]+=xx;
    Ans+=sum[col[now]]*sum[col[now]];
}

int main()
{
    n=read(),m=read();unit=sqrt(n);
    for(int i=1;i<=n;++i)
        col[i]=read(),bl[i]=(i/unit)+1;
    for(int i=1;i<=m;++i)
        ljl[i]=(Ques){0,0,read(),read(),i};
    sort(ljl+1,ljl+m+1,cmp_Q);

    int le=1,ri=0;
    for(int i=1;i<=m;++i)
    {
        while(le<ljl[i].le)Update(le,-1) ,le++;
        while(le>ljl[i].le)Update(le-1,1),le--;
        while(ri<ljl[i].ri)Update(ri+1,1),ri++;
        while(ri>ljl[i].ri)Update(ri,-1) ,ri--;

        if(ljl[i].le==ljl[i].ri){ljl[i].A=0,ljl[i].B=1;continue;}
        ljl[i].A=Ans-(ljl[i].ri-ljl[i].le+1);
        ljl[i].B=1ll*(ljl[i].ri-ljl[i].le)*(ljl[i].ri-ljl[i].le+1);
        lst gcd=__gcd(ljl[i].A,ljl[i].B);
        ljl[i].A/=gcd,ljl[i].B/=gcd;
    }
    
    sort(ljl+1,ljl+m+1,cmp_id);
    for(int i=1;i<=m;++i)
        printf("%lld/%lld
",ljl[i].A,ljl[i].B);
    return 0;
}