Add Two Numbers(C++)

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.
Example:

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

タイトルは分かりやすいですが、チェーンテーブルがどうやって実現したのか忘れてしまいました...
まずチェーン時計の知識を復習します.
学習のブログアドレス:https://www.cnblogs.com/scandy-yuan/archive/2013/01/06/2847801.html
https://blog.csdn.net/sinat_35512245/article/details/54600187
解題コードは次のとおりです.

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode* addTwoNumbers(ListNode* l1, ListNode* l2) {
        int add = 0;//  
        ListNode *listnode = new ListNode(0);
        ListNode *p1 = l1,*p2 = l2,*p3 = listnode;
        while(p1!=NULL&&p2!=NULL){
            add = p1->val+p2->val+add;
            p3->next = new ListNode(add%10);
            p3 = p3->next;
            add/=10;
            p1 = p1->next;
            p2 = p2->next;
        }
        while(p1!=NULL){
            add = p1->val+add;
            p3->next = new ListNode(add%10);
            add/=10;
            p1 = p1->next;
            p3 = p3->next;
        }
        while(p2!=NULL){
            add = p2->val+add;
            p3->next = new ListNode(add%10);
            add/=10;
            p2 = p2->next;
            p3 = p3->next;
        }
        if(add!=0)
            p3->next = new ListNode(1);
        return listnode->next;
        
    }
};