[2] Add Two Numbers

https://leetcode.com/problems/add-two-numbers/description/

• algorithms
• Medium (29.61%)
• Source Code: 2.add-two-numbers.py
• Total Accepted: 832.3K
• Total Submissions: 2.7M
• Testcase Example: '[2,4,3]\n[5,6,4]'

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.

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

class Solution(object):
    def addTwoNumbers(self, l1, l2):
        """
        :type l1: ListNode
        :type l2: ListNode
        :rtype: ListNode
        """