[Leetcode][021] Merge Two Sorted Lists (Java)

 1 　　public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
 2         ListNode dummyHead = new ListNode(-1);
 3         ListNode node = dummyHead;
 4         while (l1 != null && l2 != null) {
 5             if (l1.val <= l2.val) {
 6                 node.next = l1;
 7                 l1 = l1.next;
 8             } else {
 9                 node.next = l2;
10                 l2 = l2.next;
11             }
12             node = node.next;
13         }
14         // append the remaining list
15         node.next = (l1 != null) ? l1 : l2;
16         return dummyHead.next;
17　　}