牛客四 sequence

https://ac.nowcoder.com/acm/contest/884/C

要用线段树（$4\ast maxn$空间），不能用RMQ（$maxn\ast log（maxn）$空间），否则MLE。

#include<bits/stdc++.h>
using namespace std;
#define ll long long
const int maxn=3e6+100;

int n,a[maxn],b[maxn],pl[maxn],pr[maxn];
ll sum[maxn],ans=-1e9;

ll maxv[maxn*4],minv[maxn*4];

void build(int o,int l,int r)
{
    if(l==r)minv[o]=maxv[o]=sum[l];
    else
    {
        int m=(l+r)/2;
        build(o*2,l,m);
        build(o*2+1,m+1,r);
        maxv[o]=max(maxv[o*2],maxv[o*2+1]);
        minv[o]=min(minv[o*2],minv[o*2+1]);
    }
}

ll Max(int le,int rt,int o=1,int l=0,int r=n)
{
    ll maxx=-1e18;
    if(le<=l&&rt>=r)return maxv[o];
    else
    {
        int m=(l+r)/2;
        if(le<=m)maxx=max(Max(le,rt,o*2,l,m),maxx);
        if(rt>m)maxx=max(Max(le,rt,o*2+1,m+1,r),maxx);
        return maxx;
    }
}

ll Min(int le,int rt,int o=1,int l=0,int r=n)
{   
    ll minn=1e18;
    if(le<=l&&rt>=r)return minv[o];
    else
    {
        int m=(l+r)/2;
        if(le<=m)minn=min(Min(le,rt,o*2,l,m),minn);
        if(rt>m)minn=min(Min(le,rt,o*2+1,m+1,r),minn);
        return minn;
    } 
}

int main()
{
    //freopen("input.in","r",stdin);
    cin>>n;
    for(int i=1;i<=n;i++)scanf("%d",&a[i]);
    a[0]=a[n+1]=-1e9;
    for(int i=1;i<=n;i++)scanf("%d",&b[i]),sum[i]=sum[i-1]+b[i];
    
    stack<int> s;
    s.push(0);
    for(int i=1;i<=n;i++)
    {
        while(!s.empty() && a[s.top()]>=a[i])s.pop();
        pl[i]=s.top();
        s.push(i);
    }
    while(s.empty()==0)s.pop();
    s.push(n+1);
    for(int i=n;i>=1;i--)
    {
        while(!s.empty() && a[s.top()]>=a[i])s.pop();
        pr[i]=s.top();
        s.push(i);
    }   
    build(1,0,n);
    for(int i=1;i<=n;i++)
    {   
        if(a[i]==0)ans=max(ans,0LL);
        else if(a[i]>0)
        {
            ll l=sum[i]-Min(pl[i],i-1),r=Max(i,pr[i]-1)-sum[i];
            ans=max(ans,a[i]*(l+r));
        }
        else
        {
            ll l=sum[i]-Max(pl[i],i-1),r=Min(i,pr[i]-1)-sum[i];
            ans=max(ans,a[i]*(l+r));
        }
    }
    cout<<ans<<endl;
    return 0;
}