Leetcode 21. Merge two lists using Linked list in Java (with mistakes noted)

MY MISTAKE:
 if(list1 == null) {

    return list1;   // ❌ This should return list2, not list1

}

if(list2 == null) {

    return list2;   // ❌ This should return list1, not list2

}

👉 Reason:

• If list1 is null, that means no nodes are left in list1, so you should just return the other list (list2).

• Similarly, if list2 is null, you should return list1.
  

CODE:

class Solution {

    public ListNode mergeTwoLists(ListNode list1, ListNode list2) {

        if(list1 == null) {

            return list2;

        }

        if(list2 == null) {

            return list1;

        }

        if(list1.val < list2.val) {

            list1.next = mergeTwoLists(list1.next, list2);

            return list1;

        } else {

            list2.next = mergeTwoLists(list1, list2.next);

            return list2;

        }

    }

}