[LeetCode] Merge Two Sorted Lists

Thought:
Recursion.

Code:
public class Solution {
    public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
        if (l1 == null) return l2;
        if (l2 == null) return l1;
        if (l1.val < l2.val) {
            l1.next = mergeTwoLists(l1.next, l2);
            return l1;
        }else {           
            l2.next = mergeTwoLists(l1, l2.next);
            return l2;
        }    
    }
}