2. Add Two Numbers {Medium}

Reference: xuezhichao19970719

You are given two non-empty linked lists representing two non-negative integers. The digits are stored in reverse order 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.

Example:

Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)
Output: 7 -> 0 -> 8
Explanation: 342 + 465 = 807.

Solution:

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

class Solution:
    def addTwoNumbers(self, l1, l2):
        """
        :type l1: ListNode
        :type l2: ListNode
        :rtype: ListNode
        """
        carry = 0
        root = head = ListNode(0)
        while l1 or l2 or carry:
            l1, val1 = [l1.next, l1.val] if l1 else [0, 0]
            l2, val2 = [l2.next, l2.val] if l2 else [0, 0]
            carry, ret = divmod(val1 + val2 + carry, 10)
            head.next = ListNode(ret)
            head = head.next
        return root.next