MergeTwoSortedLists.java

import common.ListNode;

/*
 * https://leetcode.com/problems/merge-two-sorted-lists/
 */
public class MergeTwoSortedLists {
    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;
        }
    }

    public static void main(String[] args) {
        System.out.println(new MergeTwoSortedLists().mergeTwoLists(
                new ListNode(1,
                        new ListNode(2,
                                new ListNode(4))),
                new ListNode(1,
                        new ListNode(3,
                                new ListNode(4)))
        )); // 1,1,2,3,4,4
    }
}