Given a list of tasks, each composed of a start and an end time, return the maximum set of tasks which are compatible. Two tasks are compatible if they don't overlap.

struct comparator
{
    bool operator()(const std::pair<int,int> &left, const std::pair<int,int> &right)
    {
        return left.second < right.second;
    }
};
 
vector<pair<int, int>> IntervalScheduling(vector<pair<int, int>> &tasks)
{
    if (tasks.size() < 1)
        return tasks;
 
    vector<pair<int, int>> ret;
    // Sort by the end times
    sort(tasks.begin(), tasks.end(), comparator());
    // Iterate and select the immediate compatible start in a greedy manner
    ret.push_back(tasks[0]);
    for (int i = 1; i < tasks.size(); i++)
        if (ret[ret.size() - 1].second <= tasks[i].first)
            ret.push_back(tasks[i]);
    
    return ret;
}