addTwoNumbers.py

# 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
        """
        ret = ListNode(0)
        is_initial = True
        while l1.next or l2.next:
            if l1.next and not l2.next:
                ret.val = ret.val + l1.next.val
                ret.next = l1.next
                if is_initial:
                    _ret = ret
                    is_initial = False
                break
            elif not l1.next and l2.next:
                ret.val = ret.val + l2.next.val
                ret.next = l2.next
                if is_initial:
                    _ret = ret
                    is_initial = False
                break
            else:
                sum = l1.val + l2.val
                if sum < 10:
                    ret.val = ret.val + sum
                    ret.next = ListNode(0)
                else:
                    ret.val = ret.val + sum - 10
                    ret.next = ListNode(1)
                ret = ret.next
                l1 = l1.next
                l2 = l2.next
                if is_initial:
                    _ret = ret
                    is_initial = False
        return _ret
    
a1 = ListNode(5)
a2 = ListNode(8)
a3 = ListNode(2)
a4 = ListNode(9)
a1.next = a2
a2.next = a3
a3.next = a4

b1 = ListNode(5)
b2 = ListNode(8)
b3 = ListNode(2)
b1.next = b2
b2.next = b3

s = Solution()
print(s.addTwoNumbers(a1, b1))