作业十三（LeetCode第三题）

题目：Add Two Numbers

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.

Code:

# 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
        """
        if l1==None:
            return l2
        if l2==None:
            return l1
        l3=ListNode(0)
        last=l3
        carry=0
        while l1 or l2:
            sum=0
            if l1!=None:
                sum+=l1.val
                l1=l1.next
            if l2!=None:
                sum+=l2.val
                l2=l2.next
            sum+=carry
            carry=0
            if sum>=10:
                sum=sum%10
                carry=1
            last.next=ListNode(sum)
            last=last.next
        if carry:
            last.next=ListNode(1)
        last=l3.next
        del l3
        return last