Merge Two Sorted Lists

 1 /**
 2  * Definition for ListNode.
 3  * public class ListNode {
 4  *     int val;
 5  *     ListNode next;
 6  *     ListNode(int val) {
 7  *         this.val = val;
 8  *         this.next = null;
 9  *     }
10  * }
11  */ 
12 public class Solution {
13     /**
14      * @param ListNode l1 is the head of the linked list
15      * @param ListNode l2 is the head of the linked list
16      * @return: ListNode head of linked list
17      */
18     public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
19         if (l1 == null) return l2;
20         if (l2 == null) return l1;
21         
22         ListNode dummy = new ListNode(Integer.MIN_VALUE);
23         ListNode current = dummy;
24         
25         while (l1 != null && l2 != null) {
26             if (l1.val < l2.val) {
27                 current.next = l1;
28                 l1 = l1.next;
29             } else {
30                 current.next = l2;
31                 l2 = l2.next;
32             }
33             current = current.next;
34         }
35         
36         if (l1 != null) {
37             current.next = l1;
38         } else {
39             current.next = l2;
40         }
41         return dummy.next;
42     }
43 }