1 /**
 2  * Definition for singly-linked list.
 3  * class ListNode(var _x: Int = 0) {
 4  *   var next: ListNode = null
 5  *   var x: Int = _x
 6  * }
 7  */
 8 object Solution {
 9     def mergeTwoLists(l1: ListNode, l2: ListNode): ListNode = {
10         if (l1 == null) l2
11         else if (l2 == null) l1
12         else if (l1.x > l2.x) {
13             l2.next = mergeTwoLists(l1, l2.next)
14             return l2
15         } 
16         else {
17             l1.next = mergeTwoLists(l1.next, l2)
18             return l1
19         }
20     }
21 }