leetcode刷题之旅（2）Add Two Numbers

题目描述

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.

样例

Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)
Output: 7 -> 0 -> 8
Explanation: 342 + 465 = 807.

思路分析

题意即，两链表节点分别相加，考虑两链表不为空的情况下，处理进位情况，分别相加即可，其余见注释。

代码

public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
		ListNode sentinel = new ListNode(0);//创建新链表
		ListNode d = sentinel;
		int sum = 0;
		while (l1!=null || l2!=null)
		{
			sum /=10;   //sum依次与进位，l1，l2相加
			if (l1 != null) 
			{
				sum += l1.val; 
				l1 = l1.next;
			}
			if (l2 != null)
			{
				sum += l2.val; 
				l2 = l2.next;
			}
			d.next = new ListNode(sum % 10);  //d的下一节点为两数之和，注意%是保证个位数
			d = d.next;  //删除d节点，用d.next替代
		}
		if (sum/10 == 1)//考虑最后两位和大于10的情况
		{
			d.next = new ListNode(1);  //因为无后续节点，不用删除了
		}
		return sentinel.next;
	}