algo4: randomized: Quick sort partition
algo4: randomized: Quick sort related problems
algo4: randomized: quick_sort_in_place: Modified scanning direction in partition()
algo4: randomized: Quick select
algo4: randomized: Quick select medium of an unsorted array
    -- fixed bug in quick_select_top_k_numbers, we cannot by default
       choose the first element as pivot and then start off from left to right