You are given two non-empty linked lists representing two non-negative integers. The most significant digit comes first and each of their nodes contain a single digit. Add the two numbers and return it as a linked list.
You may assume the two numbers do not contain any leading zero, except the number 0 itself.
What if you cannot modify the input lists? In other words, reversing the lists is not allowed.
Input: (7 -> 2 -> 4 -> 3) + (5 -> 6 -> 4) Output: 7 -> 8 -> 0 -> 7
# 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:
stack1 = []
stack2 = []
while l1:
stack1.append(l1.val)
l1 = l1.next
while l2:
stack2.append(l2.val)
l2 = l2.next
head = None
carry = 0
while stack1 or stack2 or carry:
digit = carry
digit += stack1.pop() if stack1 else 0
digit += stack2.pop() if stack2 else 0
carry = 1 if digit > 9 else 0
digit -= 10 if digit > 9 else 0
temp = ListNode(digit)
temp.next = head
head = temp
return head