Leetcode 2 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

#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

struct ListNode
{
	int val;
	ListNode *next;
	ListNode(int x) : val(x), next(NULL) {

	}
};

class Solution {
	public:
		/*ListNode* convert(ListNode* head) {//link reverse
			ListNode* cur=head;
			ListNode* next=cur->next;
			ListNode* pre=NULL;
			ListNode* tmp = NULL;
			while(next!=NULL) {
				cur->next = pre;
				pre = cur;
				tmp = next->next;
				next->next=cur;
				cur = next;
				next = tmp;
			}

			return cur;
		}

		int listLength(ListNode* head) {// the length of the link
			int cnt = 0;
			while(head!=NULL) {
				cnt++;
				head = head->next;
			}
		}*/
		ListNode* addTwoNumbers(ListNode* l1, ListNode* l2) {
			ListNode* h1 = l1;
			ListNode* ans = NULL;
			ListNode* h2 = l2;

			ans=h1;
			int cnt = 0;
			ListNode* pre = NULL;
			
			for(; h1 != NULL && h2 != NULL; h1 = h1->next, h2=h2->next) {
				pre=h1;
				h1->val += h2->val+cnt;
				cnt = h1->val/10;
				h1->val = h1->val%10;
			}
			
			ListNode *h = h1 == NULL ? h2 : h1;

			if(h != h1) {
				pre->next = h;
			}

			for(; h!=NULL; h=h->next) {
				pre = h;
				h->val += cnt;
				cnt = h->val/10;
				h->val %= 10;
			}

			if(cnt > 0) {
				pre->next = new ListNode(cnt);
			}
			return ans;
		}
};

int main() {
	ListNode *h1 = new ListNode(1), *h2 = new ListNode(9);
	h2->next = new ListNode(9);
	Solution *s1 = new Solution();
	ListNode *ans = s1->addTwoNumbers(h1, h2);
	while(ans!=NULL) {
		cout << ans->val << " ";
		ans = ans->next;
	}
	cout << endl;
}