traverse listnode in python

Question

Can someone help me with how can I traverse through below given listnode in python. I have written this command and am getting such outputs.

list1=[1,2,4]

Command:-

print(list1)
print(list1.val)
print(list1.next.val)

OUTPUT:-

ListNode{val: 1, next: ListNode{val: 2, next: ListNode{val: 4, next: None}}}
1
2

Answer 1

To get the output you have listed at the end of your question, you would need to create a linked list. For instance, if you define the following class:

class ListNode:
    def __init__(self, val, nxt=None):
        self.val = val
        self.next = nxt

    def __repr__(self):
        return f"ListNode{{val: {self.val}, next: {self.next}}}"

And if you then define list1 as follows:

list1 = ListNode(1, ListNode(2, ListNode(4, None)))

Then the "commands" will give the output that you listed.

List to Linked List

If you want to create the above linked list from the list [1,2,4], then use this function:

def createLinkedList(values):
    head = None
    for val in reversed(values):
        head = ListNode(val, head)
    return head

Now you can convert a plain list to a linked list as follows:

list1 = createLinkedList([1,2,4])

Linked List to list

If you want to do the opposite, and create a standard list from a linked list, then define this function:

def linkedListIterator(head):
    while head:
        yield head.val
        head = head.next

Now, if you have a linked list, you can pass it to the above function. For instance:

list1 = createLinkedList([1,2,4])
lst = list(linkedListIterator(list1))

lst will be [1,2,4]