python实现快速排序

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def quick_sort(alist, start, end):
    if start >= end:
        return
    mid = alist[start]
    left = start
    right = end
    while left < right:
        while left < right and alist[right] >= mid:
            right -= 1
        alist[left] = alist[right]
        while left < right and alist[left] < mid:
            left += 1
        alist[right] = alist[left]
    alist[left] = mid
    # print(alist)

    quick_sort(alist, start, left - 1)

    quick_sort(alist, left + 1, end)


if __name__ == '__main__':
    li = [54, 26, 93, 17, 77, 31, 44, 55, 20]
    print(li)
    quick_sort(li, 0, len(li)-1)
    print(li)