快速排序python递归 [英] quick sort python recursion

问题描述

这是我的快速排序代码，partition函数运行良好，但是在调用递归时遇到问题. pos每次启动功能时都会更改，然后列表限制也将更改.该如何解决?

This is my quick sort code, the partition function works well, but I got a problem while calling the recursion. The pos changes every time it starts the function and then the list limits are change as well. How to fix that?

def partition(lst, start, end):

    pos=0
    if len(lst)<2:
        return 
    for i in range(len(lst[start:end])):
        if lst[i] < lst[end]:
            lst[i],lst[pos]=lst[pos],lst[i]
            pos+=1

        elif i==(len(lst[start:end])-1):
            lst[end],lst[pos]=lst[pos],lst[end]

    return pos

def quick_sort_recursive(lst, start, end):

        pos=partition(lst, start, end)
    if start<=pos<=end :
        quick_sort_recursive(lst, start, pos-1)
        quick_sort_recursive(lst, pos+1, end)
    else:
        return lst

推荐答案

您的代码中存在许多问题，以下是一些修复程序，它们只是为了使其正常工作:

There are numerous problems in your code, here are some fixes just to make it work:

def partition(lst, start, end):
    pos = start                           # condition was obsolete, loop won't
                                          # simply run for empty range

    for i in range(start, end):           # i must be between start and end-1
        if lst[i] < lst[end]:             # in your version it always goes from 0
            lst[i],lst[pos] = lst[pos],lst[i]
            pos += 1

    lst[pos],lst[end] = lst[end],lst[pos] # you forgot to put the pivot
                                          # back in its place
    return pos

def quick_sort_recursive(lst, start, end):
    if start < end:                       # this is enough to end recursion
        pos = partition(lst, start, end)
        quick_sort_recursive(lst, start, pos - 1)
        quick_sort_recursive(lst, pos + 1, end)
                                          # you don't need to return the list
                                          # it's modified in place

示例:

example = [3,45,1,2,34]
quick_sort_recursive(example, 0, len(example) - 1)
print example

赠予:

python test.py

python test.py

[1、2、3、34、45]

[1, 2, 3, 34, 45]

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