import statistics


def quickSort(alist):
    quickSortHelper(alist, 0, len(alist) - 1)


def quickSortHelper(alist, first, last):
    if first < last:
        splitpoint = partition(alist, first, last)

        quickSortHelper(alist, first, splitpoint - 1)
        quickSortHelper(alist, splitpoint + 1, last)


def partition(alist, first, last):
    mid = (last - first) // 2
    medianlist = [alist[first], alist[mid], alist[last]]
    median = statistics.median(medianlist)

    if median == alist[mid]:
        alist[first], alist[len(alist) // 2] = alist[len(alist) // 2], alist[first]
    elif median == alist[last]:
        alist[first], alist[last] = alist[last], alist[first]

    pivotvalue = alist[first]

    leftmark = first + 1
    rightmark = last

    done = False
    while not done:

        while leftmark <= rightmark and alist[leftmark] <= pivotvalue:
            leftmark = leftmark + 1

        while alist[rightmark] >= pivotvalue and rightmark >= leftmark:
            rightmark = rightmark - 1

        if rightmark < leftmark:
            done = True
        else:
            temp = alist[leftmark]
            alist[leftmark] = alist[rightmark]
            alist[rightmark] = temp

    temp = alist[first]
    alist[first] = alist[rightmark]
    alist[rightmark] = temp

    return rightmark


alist = [54, 26, 93, 17, 77, 31, 44, 55, 20]
quickSort(alist)
print(alist)