使用 Python 实现双向链表

Question

I'm trying to implement doubly linked list in python but am not able to implement deletion properly.

def deleteFromBeginning(self):
    if self.listLength()==0:
        print("Can't delete from an empty list")
    else:
        self.head = self.head.next

def deleteFromEnd(self):
    if self.listLength() ==0:
        print("Can't delete from an empty list")
    else:

        current=self.head
        while(current.next!=None):
            current.prev = current
            current = current.next

        current.prev.next = None
        current.prev = None

def deleteFromPosition(self,pos):
    if pos> self.listLength() or pos<0:
        ValueError("Enter a valid position")
    elif pos==0:
        deleteFromBeginning()
    elif pos == self.listLength():
        deleteFromEnd()
    else:
        if self.listLength()==0:
            print("Can't delete from an empty list")
        else:
            current=self.head
            count = 1
            while(current.next!=None and count<pos):
                current = current.next
                count = count+1

            current.prev.setNext(current.next)
            current.next.setPrev(current.prev)
            current.setPrev(None)
            current.setNext(None)

def deleteWithData(self,data):
    if self.listLength()==0:
        ValueError("Can't delete from an empty list")
    else:
        current = self.head
        while current.next!=None:
            if current.data == data:
                current.prev.next = current.next
                current.next.prev = current.prev
                return
            else:
                current = current.next
        print("The value provided is not present")

The deletion from beginning and end works fine but deletion with position and data are not giving the desired results.

Answer 1

One slight refactoring I would do is move your

if self.listLength()==0:
            print("Can't delete from an empty list")

check to the very top, and not inside the else. This should be one of the very first checks you make.

Other than that, what you can try is keep a track of the previous node:

while(current.next!=None and count<pos):
                temp = current
                current = current.next
                count = count+1

        temp.setNext(current.next)
        current.next.setPrev(temp)

This should remove the node in the x position, by relinking the previous node to the next node.

Haven't tested it, let me know how it goes!