（python）leetcode刷题笔记 02 Add Two Numbers

2. 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.

# Definition for singly-linked list.
#class ListNode:
#    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
        carry=0
        s=ListNode(0)
        ret=s
        while l1 or l2:#如果两个链表next均不为空
            sum=0
            if l1:
                sum+=l1.val
                l1=l1.next
            if l2:
                sum+=l2.val
                l2=l2.next
            sum+=carry
            s.next=ListNode(sum%10)
            s=s.next
            carry=(sum>=10)
        if carry==1:
            s.next=ListNode(1)
        del s
        return ret.next