LeetCode-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.

Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)
Output: 7 -> 0 -> 8

# 2, 4, 3 + 5, 6, 4 > 7, 0, 8
# 2, 4, 3 + 5, 6, 9 > 7, 0, 3, 1

# 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
        """
        result = root = ListNode(0)
        carry = 0
        while l1 or l2 or carry:
            sum = (l1.val if l1 else 0) + (l2.val if l2 else 0) + carry
            carry, val = divmod(sum, 10)
            result.next = ListNode(val)
            result = result.next
            l1 = l1.next if l1 else None
            l2 = l2.next if l2 else None
        return root.next

        
l1 = ListNode(2)
l1.next = ListNode(4)
l1.next.next = ListNode(3)

l2 = ListNode(5)
l2.next = ListNode(6)
l2.next.next = ListNode(9)


sln = Solution()
result = sln.addTwoNumbers(l1, l2)
while result:
    print result.val
    result = result.next

反思

1. 同时遍历多个列表的写法
2. 注意最后一次加法的进位
3. 如何生成测试用例