快速排序（递归实现）

# 快速排序
alist = [2,1,4,66,54,78]

def quick_sort(alist, start, end):
    if start>=end:
        return
    low = start
    high = end
    mid = alist[start]
    while low < high:
        while low<high and alist[high]>=mid:
            high -= 1
        alist[low] = alist[high]
        while low<high and alist[low]<=mid:
            low += 1
        alist[high] = alist[low]
    alist[low] = mid    
    quick_sort(alist, start, low-1)
    quick_sort(alist, low +1, end)

quick_sort(alist, 0, len(alist)-1)
print(alist)