Merge Two Sorted Lists

Merge two sorted linked lists and return it as a new list. The new list should be made by splicing together the nodes of the first two lists.

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode *mergeTwoLists(ListNode *l1, ListNode *l2) {
        
        ListNode *l3 = new ListNode(0);
        ListNode *p1 = l1;
        ListNode *p2 = l2;
        ListNode *p3 = l3;
        
        while(p1 != NULL && p2 != NULL)
        {
            ListNode *node = new ListNode(0);
            if(p1->val <= p2->val)
            {
                node->val = p1->val;
                p1 = p1->next;
            }
            else
            {
                node->val = p2->val;
                p2 = p2->next;
            }
            p3->next = node;
            p3 = p3->next;
            node = NULL;
        }
        
        while(p1 != NULL)
        {
            ListNode *node = new ListNode(p1->val);
            p3->next = node;
            p3 = p3->next;
            node = NULL;
            p1 = p1->next;
        }
        
        while(p2 != NULL)
        {
            ListNode *node = new ListNode(p2->val);
            p3->next = node;
            p3 = p3->next;
            node = NULL;
            p2 = p2->next;
        }
        
        ListNode *del = l3;
        l3 = l3->next;
        delete del;
        
        return l3;
    }
};