小能猫||洛谷的问题

#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;
int a[100001];
vector<int> sn,sx;
int main()
{
    int n,ans=0;
    cin>>n;
    for(int i=1;i<=n;++i)
        cin>>a[i];
    for(int i=1;i<=n;++i)
    {
        while((!sn.empty())&&(a[sn[sn.size()-1]]>=a[i])) sn.pop_back();
        while((!sx.empty())&&(a[sx[sx.size()-1]]<a[i])) sx.pop_back();
        int k=upper_bound(sn.begin(),sn.end(),sx[sx.size()-1])-sn.begin();
        if(k!=sn.size()) ans=max(ans,i-sn[k]+1);
        sn.push_back(i);
        sx.push_back(i);
    }
    cout<<ans;
    return 0;
}