2. Add Two Numbers

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.



class Solution:
    def addTwoNumbers(self, l1, l2):
        """
        :type l1: ListNode
        :type l2: ListNode
        :rtype: ListNode
        """
        if l1 is None:
            return l1
        elif l2 is None:
            return l1
        start = ListNode(0)
        temp = start
        carry = 0
        while l1 or l2:
            sum = 0
            if l1:
                sum += l1.val
                l1 = l1.next
            if l2:
                sum += l2.val
                l2 = l2.next
            sum += carry
            carry = 1 if sum>9 else 0
            temp.next = ListNode(sum % 10)
            temp = temp.next
        if carry:
            temp.next = ListNode(1)
        temp = start.next
        del start
        return temp