gistfile1.txt

# 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
        """
        
        carry = 0
        c1 = l1
        c2 = l2
        head = ListNode(None)
        last = None
        current = head
        while c1 is not None or c2 is not None or carry:
            current_sum = carry
            if c1 is not None:
                current_sum += c1.val
                c1 = c1.next
            if c2 is not None:
                current_sum += c2.val
                c2 = c2.next

            carry = 0            
            if current_sum >= 10: carry = 1
            current_sum %= 10
            
            current.val = current_sum
            current.next = ListNode(None)
            last = current
            current = current.next
        last.next = None
        return head