UVa: 231 - Testing the CATCHER

#include <algorithm>
#include <iostream>
#include <vector>

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, test = 0;
    cin >> k;
    while(k != -1)
    {
        a.clear();

        while(k != -1)
        {
            a.push_back(k);
            cin >> k;
        }

        reverse(a.begin(), a.end());

        r = vector <int> (a.size(), -1);
        t = vector <int> (1, 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];
                }
            }
        }

        if(test)
            cout << endl;

        cout << "Test #" << test+1 << ":" << endl;
        cout << "  maximum possible interceptions: " << n+1 << endl;

        cin >> k;
        test++;
    }

    return 0;
}