双向链表的实现

Question

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

class DoublyLinkedList:
    def __init__(self):
        self.head = None
        self.tail = None
        self.count = 0

    def insertStart(self, data):
        nn = Node(data)
        self.count +=1
        if(self.head==None):
            self.head = nn
            self.tail = nn
            return
        nn.next = self.head
        self.head.prev = nn
        self.head = nn

    def insertEnd(self, data):
        nn = Node(data)
        self.count +=1
        if(self.tail is None):
            self.head = nn
            self.tail = nn
            return

        nn.prev = self.tail
        self.tail.next = nn
        self.tail = nn

    def insertAtPos(self, data, pos):
        nn = Node(data)
        if(self.count < pos):
            return -1

        mid = int(self.count/2)
        # print(mid)

        if(pos<=mid):
            temp = self.head
            for i in range(1, pos-1):
                temp = temp.next

            nn.next = temp.next
            nn.prev = temp
            temp.next = nn
        else:
            temp = self.tail
            for i in range(self.count-1, pos, -1):
                temp = temp.prev

            print(temp.data)
            nn.prev = temp.prev
            nn.next = temp
            temp.prev = nn

        self.count += 1



    def removeStart(self):
        self.count -=1
        if(self.head is None):
            return -1

        if(self.count == 1):
            self.head = None
            self.tail = None

        self.head = self.head.next
        self.head.prev = None

    def removeEnd(self):
        self.count -=1
        if(self.tail is None):
            return -1

        self.tail = self.tail.prev
        self.tail.next = None


    def display(self):
        temp = self.head
        while(temp is not None):
            print(temp.data)
            temp = temp.next


    dd = DoublyLinkedList()

    dd.insertEnd(40)
    dd.insertStart(22)
    dd.insertEnd(42)
    dd.insertStart(20)
    dd.insertStart(23)
    # dd.display()
    print()
    dd.removeStart()
    dd.removeEnd()
    dd.display()
    print()
    dd.insertAtPos(33, 3)
    dd.display()

In the insertAtPos function, my else part is not inserting the new node, everything seems to work fine but when I use display function new node that is added is not appearing. There's some problem in the else part. Please help!

Answer 1

In else part, you forgot to add:

temp.prev.next = nn

And change for loop in else part to:

for i in range(self.count, pos, -1):