UVa: 481 - What goes up

#include <iostream>
#include <vector>
#include <stack>

using namespace std;

vector <int> a, t, r;
int n;

///La idea es que ceil me busque el menor valor que es mayor al dado
int ceil(int v)
{
    if(v > a[t[n]])
        return -1;
    int s = 0, e = n;
    while(s+1 < e)
    {
        int m = (s+e)/2;
        if(a[t[m]] > v)
            e = m;
        else
            s = m;
    }
    if(a[t[s]] > v)
        return s;
    return e;
}

int main()
{
    int k;
    while(cin >> k)
        a.push_back(k);

    r = vector <int> (a.size(), -1);
    t.push_back(0);
    n = 0;

    for(int i=1; i<a.size(); i++)
    {
        if(a[i] > a[t[n]])
        {
            r[i] = t[n];
            t.push_back(i);
            n++;
        }
        else
        {
            int p = ceil(a[i]);
            if(p >= 0 && p <= n)
            {
                t[p] = i;
                if(p)
                    r[i] = t[p-1];
            }
        }
    }

    stack <int> res;
    int p = t[n];
    while(p != -1)
    {
        res.push(a[p]);
        p = r[p];
    }

    cout << res.size() << endl << "-" << endl;
    while(res.size())
    {
        cout << res.top() << endl;
        res.pop();
    }

    return 0;
}