021. Merge Two Sorted Lists

/********************
// 021. 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.
// Example:
// Input: 1->2->4, 1->3->4
// Output: 1->1->2->3->4->4
********************/

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
class Solution {
    public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
        ListNode head = new ListNode(0);
        ListNode p = head;
 
        while(l1 != null && l2 != null) {
            if(l1.val < l2.val) {
                p.next = l1;
                l1 = l1.next;
            }else {
                p.next = l2;
                l2 = l2.next;
            }
            p = p.next;
        }
        
        if(l1 != null) {
            p.next = l1;
        }
        
        if(l2 != null) {
            p.next = l2;
        }
 
        return head.next;
    }
}