在链表末尾添加项目会产生奇怪的结果

Question

下面是我的节点类

class Node: 
    def __init__(self):
        self.data = None
        self.next = None
    
    def get_data(self):
        return self.data
    
    def set_data(self, data):
        self.data = data
        
    def get_next(self):
        return self.next
    
    def set_next(self, node):
        self.next = node

下面是我的带有插入方法的链表类

class SingleyLinkedList:
    
    def __init__(self):
        self.head = Node()
    
    def insertAtHead(self, data):
        currentNode = self.head

        newNode = Node()
        newNode.set_data(data)  
        
        if currentNode != None:
            newNode.set_next(currentNode)
            self.head = newNode
            print("Inserted ", data, " at the head")
        else:
            self.head.set_next(newNode)
    
    def insertAtEnd(self, data):
        currentNode = self.head
        
        new_node = Node()
        new_node.set_data(data)
        
        while currentNode.get_next() != None:
            currentNode = currentNode.next
        
        currentNode.set_next(new_node)
        print("Inserted ", data, " at end")
    
    def printNode(self):
        print("\nPrinting the nodes")
        currentNode = self.head
        
        while currentNode.next != None:
            print(currentNode.data, " --> ", end="")
            currentNode = currentNode.next
        print(" NULL \n")

s = SingleyLinkedList()

s.insertAtHead(5)
s.printNode()

s.insertAtHead(10)
s.printNode()

s.insertAtHead(1)
s.printNode()

s.insertAtEnd(20)
s.printNode()

我得到以下结果，

端部插入20

正在打印节点1-->10-->5-->none->NULL

Answer 1

首先用node()初始化head，其中包含none值，这是不正确的，您应该有空head，这就是为什么您在末尾看到none，因为它会传播到末尾，最后，您没有打印最后一个node()，因为最后一个节点没有next这个条件不显示nodenext：

    while currentNode.next != None:
        print(currentNode.data, " --> ", end="")
        currentNode = currentNode.next

所以你需要再打印一张。

下面的工作示例进行了小的简化：

class Node:
    def __init__(self, data=None, next=None):
        self.data = data
        self.next = next

    def get_data(self):
        return self.data

    def set_data(self, data):
        self.data = data

    def get_next(self):
        return self.next

    def set_next(self, node):
        self.next = node


class SingleyLinkedList:

    def __init__(self):
        self.head = None

    def insertAtHead(self, data):
        old_head = self.head
        self.head = Node(data, old_head)
        print("Inserted ", data, " at the head")


    def insertAtEnd(self, data):
        currentNode = self.head

        while currentNode.get_next() != None:
            currentNode = currentNode.next

        currentNode.set_next(Node(data))
        print("Inserted ", data, " at end")


    def printNode(self):
        print("\nPrinting the nodes")
        currentNode = self.head

        while currentNode.next != None:
            print(currentNode.data, " --> ", end="")
            currentNode = currentNode.next
        print(currentNode.data, " --> ", end="")
        print(" NULL \n")


s = SingleyLinkedList()

s.insertAtHead(5)
s.printNode()

s.insertAtHead(10)
s.printNode()

s.insertAtHead(1)
s.printNode()

s.insertAtEnd(20)
s.printNode()

Inserted  5  at the head

Printing the nodes
5  -->  NULL 

Inserted  10  at the head

Printing the nodes
10  --> 5  -->  NULL 

Inserted  1  at the head

Printing the nodes
1  --> 10  --> 5  -->  NULL 

Inserted  20  at end

Printing the nodes
1  --> 10  --> 5  --> 20  -->  NULL