https://leetcode.com/problems/add-two-numbers/
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
这道题思路比较简单，两个链表从头到尾相加即可。容易出错的地方是最后两个链表走完要记得check offset是否为0. 不为0还要加上一个node. 此外这种从头构造链表的题目，技巧是加一个dummy node。代码如下，时间复杂度O(n), 空间复杂度O(1)
1 /** 2 * Definition for singly-linked list. 3 * public class ListNode { 4 * int val; 5 * ListNode next; 6 * ListNode(int x) { val = x; } 7 * } 8 */ 9 public class Solution { 10 public ListNode addTwoNumbers(ListNode l1, ListNode l2) { 11 ListNode dummy = new ListNode(0); 12 ListNode tail = dummy; 13 int offset = 0; 14 while(l1 != null || l2 != null){ 15 int total = 0; 16 if(l1 != null){ 17 total += l1.val; 18 l1 = l1.next; 19 } 20 if(l2 != null){ 21 total += l2.val; 22 l2 = l2.next; 23 } 24 total += offset; 25 ListNode node = new ListNode(total%10); 26 offset = total / 10; 27 tail.next = node; 28 tail = node; 29 } 30 if(offset != 0){ 31 ListNode node = new ListNode(offset); 32 tail.next = node; 33 } 34 return dummy.next; 35 } 36 }
原文：http://www.cnblogs.com/xinhuan23/p/5178876.html