CODEWITHSUNDEEP
pythonclasslinked-listreference
Vindic
Vindic

Reputation: 25

Python method not modifying in place

I am trying to implement a linked list class from scratch in Python, and am encountering an issue that is probably related to how Python is intended to work, but I would like to make sure.

Here is the basis of my implementation:

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

    def appendToTail(self, d: int):
        newNode = Node(d)
        while self.next is not None: self = self.next
        self.next = newNode

And the class method that does not work as I would like it to :

    def reverse(self):
        prevNode = None
        currentNode = self # current = 1
        while self is not None:
            nextNode = self.next
            self.next = prevNode
            prevNode = self
            self = nextNode
        self = prevNode

I am trying to reverse the linked list in place, but when I call this method, the list appears to be empty. I also implemented another version of this method that preforms a return self at the end, and the returned list is indeed the correct result I am looking for:

def reverseNotInPlace(n: Node()) -> Node():
    prevNode = None
    n = n.next
    while n is not None:
        nextNode = n.next
        n.next = prevNode
        prevNode = n
        n = nextNode
    return prevNode

To summarize:

# creating a linked list such as: [1 -> 2 -> 3]
myList = Node()
myList.appendToTail(1)
myList.appendToTail(2)
myList.appendToTail(3)

# inverting it not in place works
invList = reverseNotInPlace(myList)
# returns [3 -> 2 -> 1]

myList.reverse()
# returns only the first node of myList()

So my question is: is there something wrong with my implementation ? Or is what I am trying to do not exactly possible ?

Thank you very much !

Upvotes: 0

Views: 115

Answers (1)

ddlr
ddlr

Reputation: 323

There is a logical error with your first approach. Your Node class must not have a reverse method. Since reversing a node does not actually make any sense. In fact reversing a link list does make sense.

So it is better divide your code in two parts:

  1. Your node class having a constructor to initialise a node
  2. A linked list class with functions to append a node to end and for reversing a linked list. Also pass the head of the linked list to both of these functions

Upvotes: 1

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