package amazon;

import entity.ListNode;

// 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

/**

* Definition for singly-linked list.

* public class ListNode {

* int val;

* ListNode next;

* ListNode(int x) { val = x; }

* }

*/

/**

* leetcode 2 -> https://leetcode.com/problems/add-two-numbers

* 扩展:https://leetcode.com/problems/add-two-numbers-ii/

*/

public class AddTwoNumbers {

public ListNode addTwoNumbers(ListNode l1, ListNode l2) {

ListNode dummy = new ListNode(0);// 哨兵节点，用来做返回值的头结点使用。

ListNode tail = dummy; // 用一个tail指针来操作dummy的下一个节点

int sum = 0; // 每次遍历两个链表的和

while (l1 != null || l2 != null) {

sum /= 10; // 每次进来之后都取上次sum的十位

if (l1 != null) {

sum += l1.val;

l1 = l1.next;

}

if (l2 != null) {

sum += l2.val;

l2 = l2.next;

}

tail.next = new ListNode(sum % 10);// 尾插新节点，新节点的值为sum的个位数，十位进一

tail = tail.next;

}

if (sum / 10 == 1) {

tail.next = new ListNode(1);

}

return dummy.next;

}

}