Monotonic Queue [prvi '<']

#include <bits/stdc++.h>
using namespace std;

const int N=1e5+10;

int a[N], f[N][2], n;
stack<int> box;

int main()
{
    scanf ("%d", &n);
    for (int i=1;i<=n;i++) scanf ("%d", &a[i]);

    for (int i=1;i<=n;i++)
    {
        while (!box.empty())
        {
            int xt=box.top();
            if (a[xt]>a[i])
            {
                f[i][0]=xt;
                break;
            }
            else box.pop();
        }

        box.push(i);
    }

    while (!box.empty()) box.pop();

    for (int i=n;i>0;i--)
    {
        while (!box.empty())
        {
            int xt=box.top();
            if (a[xt]>a[i])
            {
                f[i][1]=xt;
                break;
            }
            else box.pop();
        }

        box.push(i);
    }

    return 0;
}