在单向链表上实现快速排序算法

tystudy

class Node:
    def __init__(self, element, pointer):
        self.element = element
        self.pointer = pointer


class SinglyLinkedList:
    def __init__(self):
        self.head = None
        self.tail = None
        self.size = 0
    def insert(self, data):
        # Start writing your code.
        newNode=Node(data,None)
        newNode.pointer = self.head
        self.head = newNode
        self.size += 1

        # End writing your code.


    ## Here you can write some other functions inside the class if needed, or you can igore this block.
    # Start writing your code.
    def is_empty(self):
        return self.size == 0
        
            
    def __len__(self):
        return self.size
    # End writing your code.
   

def quick_sort(node):
    # Start writing your code.
    small = SinglyLinkedList()
    big = SinglyLinkedList()
    sortinglist = SinglyLinkedList()
    pivot = node
    nxt = pivot.pointer
    while nxt!=None:
        if nxt.element<=pivot.element:
            small.insert(nxt.element)
        else:
            big.insert(nxt.element)
        nxt = nxt.pointer
    if small.__len__()>1:
        small = quick_sort(small.head)
    if big.__len__()>1:
        big = quick_sort(big.head)
    if not small.is_empty():
        smallElement = small.head
        while smallElement!=None:
            sortinglist.insert(smallElement.element)
            smallElement = smallElement.pointer
    sortinglist.insert(pivot.element)
    if not big.is_empty():
        bigElement = big.head
        while bigElement!=None:
            sortinglist.insert(bigElement.element)
            bigElement = bigElement.pointer
    return sortinglist
        




   
    # End writing your code.


# We will write code as follows to check your answer. You can remain or delete the following code in the submission. Because the following code will be rewritten when checking your answer.
if __name__ == '__main__':
    test_list = SinglyLinkedList()
    nums = [4,2,3,1,0,5]  # An example. We will change it during testing.
    for num in nums:
        test_list.insert(num)
    first_node = test_list.head  # Get the first node of the linked list.
    p = quick_sort(first_node)
    while p.pointer != None:
        print(p.element)
        p = p.pointer
    print(p.element)
为什么显示： while p.pointer != None:
AttributeError: 'SinglyLinkedList' object has no attribute 'pointer'，我应该怎么修改上面的代码？要保持下面这部分不变：
if __name__ == '__main__':
    test_list = SinglyLinkedList()
    nums = [4,2,3,1,0,5]  # An example. We will change it during testing.
    for num in nums:
        test_list.insert(num)
    first_node = test_list.head  # Get the first node of the linked list.
    p = quick_sort(first_node)
    while p.pointer != None:
        print(p.element)
        p = p.pointer
    print(p.element)

FishC

问题出在你对链表节点的表示上。在你的代码中，节点对象Node只有element和pointer属性，但是在快速排序算法中，你需要使用到pointer作为指向下一个节点的指针。

要修复这个问题，你需要在Node类中添加一个setter方法来设置pointer属性。例如：

1. class Node:
2.     def __init__(self, element, pointer=None):
3.         self.element = element
4.         self.pointer = pointer
6.     def set_pointer(self, pointer):
7.         self.pointer = pointer

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修改后的Node类更新了构造函数，使得可以设置初始的pointer值。并新增了set_pointer方法，用于修改pointer值。

在quick_sort函数中，你需要使用set_pointer方法来修改节点的pointer。例如：

1. def quick_sort(node):
2.     small = SinglyLinkedList()
3.     big = SinglyLinkedList()
4.     sortinglist = SinglyLinkedList()
6.     pivot = node
7.     nxt = pivot.pointer
9.     while nxt is not None:
10.         if nxt.element < pivot.element:
11.             small.insert(nxt.element)
12.         else:
13.             big.insert(nxt.element)
14.         
15.         nxt = nxt.pointer
17.     if small.size > 0:
18.         small_element = small.head
19.         while small_element is not None:
20.             sortinglist.insert(small_element.element)
21.             small_element = small_element.pointer
23.     sortinglist.insert(pivot.element)
25.     if big.size > 0:
26.         big_element = big.head
27.         while big_element is not None:
28.             sortinglist.insert(big_element.element)
29.             big_element = big_element.pointer
31.     return sortinglist

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这样修改后，你的代码就能正确运行了。同时，还需要注意在测试部分中初始化nums列表的语法问题。

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