LeetCode: Add Two Numbers

solution.py

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class Solution:
    def addTwoNumbers(self, l1: ListNode, l2: ListNode) -> ListNode:
        # traversing both nodes together and adding the last digit if carry is generated
        pnode = result = ListNode(None)
        carry = 0
        while l1 or l2 or carry:
            # in certain cases carry is remian but nodes are traversed
            if l1:
                carry += l1.val
                l1 = l1.next
            
            if l2:
                carry += l2.val
                l2 = l2.next
                
            pnode.next = ListNode(carry%10)
            pnode = pnode.next
            # if the carry was > 10 then it will return the 10's digit
            # else carry will get set to zero because it has been already utilized
            carry //= 10
            
        return result.next