[JZOJ1746]奶牛排队

分治

#include<bits/stdc++.h>
using namespace std;
const int N=1e6;
#define ll long long
long long  tmin[N],tmax[N],h[N],ans;
void mk(int o,int l,int r){
    if(l==r){
    tmin[o]=tmax[o]=l;
    }else{
        int mid=(r+l)/2;
        mk(o*2,l,mid);
        mk(o*2+1,mid+1,r);
        ll t1,t2;
        t1=tmin[o*2];
        t2=tmin[o*2+1];
        if(h[t1]>=h[t2])tmin[o]=t2;
        else tmin[o]=t1;
        t1=tmax[o*2];
        t2=tmax[o*2+1];
        if(h[t1]>=h[t2])tmax[o]=t1;
        else tmax[o]=t2;
    }
}
ll ppmin,ppmax,ql,qr;
void qz(int o,int l,int r){
    if(ql<=l&&r<=qr){
    int dot=tmax[o];
    
    if(h[dot]>h[ppmax])ppmax=dot;
    
    dot=tmin[o];
    if(h[dot]<=h[ppmin])ppmin=dot;
    }else{
    int m=(r+l)/2;
    if(ql<=m)qz(o*2,l,m);
    if(qr>m)qz(o*2+1,m+1,r);}
}
ll n;
void work(int l,int r){
    if(l>=r)return;
    if(l<=0)return;
    if(r<=0)return;
    ppmin=200000;
    ppmax=0;
    ql=l;qr=r;
    qz(1,1,n);
    ll pmax=ppmax;
    ll pmin=ppmin;
    if(pmin<pmax){
    work(l,pmin-1);
    work(pmax+1,r);
    ans=max(ans,pmax-pmin+1);
    return;
    }else{
    work(l,pmax);
    work(pmax+1,pmin-1);
    work(pmin,r);
    return;
    }
}
int main(){
    h[200000]=10000000000000;
    ppmin=200000;
    ios::sync_with_stdio(0);
    //freopen("p.in","r",stdin);
    //freopen("p.out","w",stdout);
    cin>>n;
    for(int i=1;i<=n;i++)
    cin>>h[i];
    mk(1,1,n);
    work(1,n);
    cout<<ans;
    return 0;
}