2、Add Two Numbers

题目描述：
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.

思路：
把链表中数据转换为整数相加，将结果放入链表中输出

当前解法：

# Definition for singly-linked list.# class ListNode:#     def __init__(self, x):#         self.val = x#         self.next = Noneclass Solution:    def addTwoNumbers(self, l1, l2):        """        :type l1: ListNode        :type l2: ListNode        :rtype: ListNode        """        # 将链表中的数转换到list中        list1 = []        list2 = []        while l1 is not None:            list1.append(l1.val)            l1 = l1.next        while l2 is not None:            list2.append(l2.val)            l2 = l2.next        # 将list两个整数相加        num1 = 0        num2 = 0        for i in range(len(list1) - 1, -1, -1):            num1 = num1 * 10 + list1[i]        for j in range(len(list2) - 1, -1, -1):            num2 = num2 * 10 + list2[j]        num3 = num1 + num2        # 将num3写入链表返回        l3 = ListNode(None)        l3.val = num3 % 10        temp = l3        while num3 >= 10:            num3 = num3 // 10            temp.next = ListNode(None)            temp.next.val = int(num3) % 10            temp = temp.next        return l3