Merge Two Sorted Lists.java

/*
Merge two sorted linked lists and return it as a new list. The new list should be made by splicing together the nodes of the first two lists.
*/

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) {
 *         val = x;
 *         next = null;
 *     }
 * }
 */
public class Solution {
    public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
        // Note: The Solution object is instantiated only once and is reused by each test case.
        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(l2.next, l1);
            return l2;
        }
    }
}