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

/**
 * 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) {
        
        ListNode *l3 = new ListNode(0);
        ListNode *p1 = l1;
        ListNode *p2 = l2;
        ListNode *p3 = l3;
        
        int carry = 0;
        int sum = 0;
        while(p1 != NULL && p2 != NULL)
        {
            sum = p1->val + p2->val + carry;
            ListNode *node = new ListNode(sum % 10);
            p3->next = node;
            p3 = node;
            
            carry = sum / 10;
            node = NULL;
            
            p1 = p1->next;
            p2 = p2->next;
        }
        
        while(p1 != NULL)
        {
            sum = p1->val + carry;
            ListNode *node = new ListNode(sum % 10);
            p3->next = node;
            p3 = node;
            
            carry = sum / 10;
            node = NULL;
            
            p1 = p1->next;
        }
        
        while(p2 != NULL)
        {
            sum = p2->val + carry;
            ListNode *node = new ListNode(sum % 10);
            p3->next = node;
            p3 = node;
            
            carry = sum / 10;
            node = NULL;
            
            p2 = p2->next;
        }
        
        if(carry != 0)
        {
            ListNode *node = new ListNode(carry);
            p3->next = node;
            p3 = node;
            
            node = NULL;
        }
        
        ListNode *del = l3;
        l3 = l3->next;
        delete del;
        
        return l3;
    }
};