原题地址：https://oj.leetcode.com/problems/add-two-numbers/
题意：
You are given two linked lists representing two non-negative numbers. 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.
Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)
Output: 7 -> 0 -> 8
解题思路：链表的基本操作。Two methods are provided. Method 1 is much slimmer
# Definition for singly-linked list. # class ListNode: # def __init__(self, x): # self.val = x # self.next = None class Solution: # @return a ListNode def addTwoNumbers(self, l1, l2): # method 1: 14 Lines dummy, flag = ListNode(0), 0 head = dummy while flag or l1 or l2: node = ListNode(flag) if l1: node.val += l1.val l1 = l1.next if l2: node.val += l2.val l2 = l2.next flag = node.val / 10 node.val %= 10 head.next = node head = head.next # head.next, head = node, node return dummy.next """ # method 2: 24 Lines if not l1: return l2 if not l2: return l1 dummy = ListNode(0) p = dummy flag = 0 while l1 and l2: tmp = l1.val + l2.val + flag p.next = ListNode( tmp % 10 ) flag = tmp / 10 l1, l2, p = l1.next, l2.next, p.next if l1: while l1: tmp = l1.val + flag p.next = ListNode( tmp % 10 ) flag = tmp / 10 l1, p = l1.next, p.next if l2: while l2: tmp = l2.val + flag p.next = ListNode( tmp % 10 ) flag = tmp / 10 l2, p = l2.next, p.next if flag == 1: p.next = ListNode(flag) return dummy.next """