445. Add Two Numbers II ——while s1 or s2 or carry 题目再简单也要些测试用例

You are given two linked lists representing two non-negative numbers. The most significant digit comes first 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.

Follow up:
What if you cannot modify the input lists? In other words, reversing the lists is not allowed.

Example:

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

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

7->2->4->3
   5->6->4
=-------------
7->7->0->7
 ->1       
        """
        s1,s2 = [],[]
        p1,p2 = l1,l2
        while p1:
            s1.append(p1.val)
            p1 = p1.next
        while p2:
            s2.append(p2.val)
            p2 = p2.next
        carry = 0
        fake_head = ListNode(None)
        while s1 or s2 or carry:
            v1 = s1.pop() if s1 else 0
            v2 = s2.pop() if s2 else 0
            val = v1 + v2 + carry
            if val >= 10:
                val -= 10
                carry = 1
            else:
                carry = 0
            head = ListNode(val)
            head.next = fake_head.next
            fake_head.next = head
        return fake_head.next