题目描述：

给定两个链表，输出两个链表的和，具体形式如下：
Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)
Output: 7 -> 0 -> 8
Explanation: 342 + 465 = 807.

解题思路：

首先分别计算出每个链表的数字(342 and 465)，然后在进行相加，把相加后的每一位存放进新的链表中。最后处理一下最高进位。python 代码如下：

class Solution(object):
    def addTwoNumbers(self, l1, l2):
        """
        :type l1: ListNode
        :type l2: ListNode
        :rtype: ListNode
        """
        rest = ListNode(0)
        ans = rest
        
        suml = 0
        i = 1
        while l1 != None:
            suml += l1.val * i
            l1 = l1.next
            i *= 10
        
        i = 1
        while l2 != None:
            suml += l2.val * i
            l2 = l2.next
            i *= 10
            
        while suml != 0:
            ans.val = suml % 10
            suml /= 10
            if suml != 0:
                ans.next = ListNode(0)
                ans = ans.next
            
        return rest