链式A+B

题目描述
有两个用链表表示的整数，每个结点包含一个数位。这些数位是反向存放的，也就是个位排在链表的首部。编写函数对这两个整数求和，并用链表形式返回结果。

给定两个链表ListNode* A，ListNode* B，请返回A+B的结果(ListNode*)。

测试样例：
{1,2,3},{3,2,1}
返回：{4,4,4}

solution:

# -*- coding:utf-8 -*-
class ListNode:
    def __init__(self, x):
        self.val = x
        self.next = None


class Plus:
    def plusAB(self, a, b):
        carry = 0
        pre = ListNode(0)
        work = pre
        while a and b:
            temp = a.val + b.val + carry
            if temp>9:
                temp -= 10
                carry = 1
            else:
                carry = 0
            new = ListNode(temp)
            work.next = new
            work = work.next
            a = a.next
            b = b.next
        while a:
            temp = a.val + carry
            if temp>9:
                temp -= 10
                carry = 1
            else:
                carry = 0
            new = ListNode(temp)
            work.next = new
            work = work.next
            a = a.next
        while b:
            temp = b.val + carry
            if temp>9:
                temp -= 10
                carry = 1
            else:
                carry = 0
            new = ListNode(temp)
            work.next = new
            work = work.next
            b = b.next
        if carry==1:
            new = ListNode(1)
            work.next = new
        return pre.next