21 Merge Two Sorted Lists

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
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;
    	}
    }
}