LeetCode2:Add Two Numbers

题目

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.

Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)
Output: 7 -> 0 -> 8

给定两个非空链表，是一个数的逆序表示

比如 2->4->3 表示 342,5->6->4表示465

现在要求他们的和，和也用逆序链表表示。

思路

先初始化一个新链表ret，让cur指向ret，然后动态变化cur

模拟人的思路，一位一位对应的去求和，存到当前位的和存到sum中

这里有一个技巧，求和的结果sum%10作为当前位置的值，sum/10作为进位的标识

代码

public class Solution {    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {        ListNode ret = new ListNode(0);        ListNode cur = ret;        int sum = 0;        while (true) {            if (l1 != null) {                sum += l1.val;                l1 = l1.next;            }            if (l2 != null) {                sum += l2.val;                l2 = l2.next;            }            cur.val = sum % 10;            sum /= 10;            if (l1 != null || l2 != null || sum != 0) {                cur = (cur.next = new ListNode(0));            } else {                break;            }        }        return ret;     }}