[BZOJ4241]历史研究

#include<cstdio>
#include<cstring>
#include<iostream>
#include<cmath>
#include<algorithm> 
using namespace std;
struct xxx{
    int l,r,lr,lblock,rblock,id;
}q[101000];
struct xxx2{
    int a,id;
}data[101000];
int cnt[101000],a[101000],b[101000],cnt2[101000];long long ans[101000];
bool cmp(xxx a,xxx b){return a.lblock!=b.lblock?a.lblock<b.lblock:a.r<b.r;}
bool cmp2(xxx2 a,xxx2 b){return a.a<b.a;}
int main()
{
    int n,Q;scanf("%d%d",&n,&Q);int T=(int)sqrt((double)n);
    for(int i=1;i<=n;i++){scanf("%d",&data[i].a);data[i].id=i;}
    sort(data+1,data+n+1,cmp2);
    int last=0;
    for(int i=1;i<=n;i++)
    {
        if(data[i].a==data[i-1].a)a[data[i].id]=last;
        else a[data[i].id]=++last;
        b[data[i].id]=data[i].a;
    }
    for(int i=1;i<=Q;i++)
    {
        scanf("%d%d",&q[i].l,&q[i].r);
        q[i].lblock=(q[i].l-1)/T+1;q[i].rblock=(q[i].r-1)/T+1;
        q[i].id=i;q[i].lr=T*q[i].lblock;
    }
    sort(q+1,q+Q+1,cmp);
    int l=1,r=0;long long Max=-1;
    for(int i=1;i<=Q;i++)
    {
        if(q[i].lblock==q[i].rblock)
        {
            for(int j=q[i].l;j<=q[i].r;j++){cnt2[a[j]]++;ans[q[i].id]=max(ans[q[i].id],1ll*cnt2[a[j]]*b[j]);}
            for(int j=q[i].l;j<=q[i].r;j++)cnt2[a[j]]--;continue;
        }
        if(q[i].lr!=l){l=q[i].lr,r=q[i].lr-1;memset(cnt,0,sizeof(cnt));Max=-1;}
        while(r<q[i].r){cnt[a[++r]]++;Max=max(Max,1ll*cnt[a[r]]*b[r]);}
        long long Max2=Max;int _l=l;
        while(_l>q[i].l){cnt[a[--_l]]++;Max=max(Max,1ll*cnt[a[_l]]*b[_l]);}
        for(int j=q[i].l;j<l;j++)cnt[a[j]]--;
        ans[q[i].id]=Max;Max=Max2;
    }
    for(int i=1;i<=Q;i++)printf("%lld\n",ans[i]);
    return 0;
}