Longest Increasing Subsequence

int pos(std::vector<int> &tail, unsigned int lhs, unsigned int rhs, int key)
{
    while(rhs - 1 > lhs)
    {
        int mid = lhs + (rhs - lhs) / 2;
        tail[mid] > key ? rhs = mid : lhs = mid;
    }

    if(rhs == tail.size() - 1)
        tail.push_back(INF);

    return rhs;
}

int LISLen(std::vector<int> &seq)
{
    std::vector<int> tail(3);
    tail[0] = -INF, tail[1] = seq[0], tail[2] = INF;

    for(unsigned int i = 1; i < seq.size(); i++)
        tail[pos(tail, tail.size(), seq[i])] = seq[i];

    return tail.size() - 2;
}