双vector单调栈求调

#include<bits/stdc++.h>
#define us unsigned
#define ll long long
using namespace std;
ll a[100010];
vector<ll> mn,mx;
int n;
ll ans;
int main(){
    cin>>n;
    for(int i=1;i<=n;i++)
        cin>>a[i];
    for(int i=1;i<=n;i++){
        while(!mx.empty()) {
            if(a[mx.back()]<a[i]) mx.pop_back();
            else break;
        }
        while(!mn.empty()) {
            if(a[mn.back()]>=a[i]) mn.pop_back();
            else break;
        }
        if(!mx.empty()){
            int k=upper_bound(mn.begin(),mn.end(),mx.back())-mn.begin();
            if (k != mn.size()+1)ans=max(ans,i-mn[k]+1);
        }
        mx.push_back(i);
        mn.push_back(i);
    }
    cout<<ans;
    return 0;
}