leetcode445 Add Two Numbers II

 """
 You are given two non-empty linked lists representing two non-negative integers. 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
 """
 """
 与leetcode2 类似。
 这两题都是自己做出来的
 """
 class ListNode:
     def __init__(self, x):
         self.val = x
         self.next = None

 class Solution:
     def addTwoNumbers(self, l1, l2):
         num1, num2 = 0, 0
         if l1 and not l2:
             return l1
         if l2 and not l1:
             return l1
         p1, p2 = l1, l2 #将链表l1 和 l2 转成数字num1 和num2 求和得num
         while p1:
             num1 = num1 * 10 + p1.val
             p1 = p1.next
         while p2:
             num2 = num2 * 10 + p2.val
             p2 = p2.next
         num = num1 + num2
         res = ListNode(0)  #头结点
         end = ListNode(num % 10) #尾结点
         res.next = end
         end.next = None
         num = num // 10
         while num:  #从链表尾部插入当前结点cur
             cur = ListNode(num % 10) #当前结点
             res.next = cur
             cur.next = end
             end = cur
             num = num // 10
         return res.next