LeetCode-21 Merge Two Sorted Lists Solution (with Java)

 1 /**
 2  * Created by sheepcore on 2019-05-07
 3  * Definition for singly-linked list.
 4  * public class ListNode {
 5  *     int val;
 6  *     ListNode next;
 7  *     ListNode(int x) { val = x; }
 8  * }
 9  */
10 class Solution {
11     public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
12         ListNode head = new ListNode(-1);
13         ListNode p = l1, q = l2, tail = head;
14         while (p != null && q != null){
15             if(p.val <= q.val){
16                 tail.next  = p;
17                 p = p.next;
18                 tail = tail.next;
19             } else{
20                 tail.next = q;
21                 q = q.next;
22                 tail = tail.next;
23             }
24         }
25         if(p != null)
26             tail.next = p;
27         if(q != null)
28             tail.next = q;
29         return head.next;
30     }
31 }