Leetcode 21. Merge Two Sorted 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* ptrFirst = l1;
        ListNode* ptrSecond = l2;
        ListNode* head = new ListNode(0);
        ListNode* current = head;
        while(ptrFirst && ptrSecond) {
            if(ptrFirst->val > ptrSecond->val) {
                current->next = ptrSecond;
                ptrSecond = ptrSecond->next;
            }
            else {
                current->next = ptrFirst;
                ptrFirst = ptrFirst->next;
            }
            current = current->next;
        }
        if(ptrFirst) {
            current->next = ptrFirst;
        }
        if(ptrSecond) {
            current->next = ptrSecond;
        }
        return head->next;
    }
};