排序算法-快速排序

def quick_sort(alist, first, last):
    '''快速排序'''
    if first >= last:
        return
    mid_value = alist[first]
    low = first
    high = last

    while low < high:
        # 让high的游标左移，当high对应的值小于基准元素
        while low < high and alist[high] >= mid_value:
            high -= 1
        alist[low] = alist[high]

        while low < high and alist[low] < mid_value:
            low += 1
        alist[high] = alist[low]
    # 从循环退出时，low = high
    alist[low] = mid_value
    # 对low左边的列表执行快速排序
    quick_sort(alist, first, low-1)
    # 对low右边的列表执行快速排序
    quick_sort(alist, low+1, last)