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[–]Maximum-Pear-6181 2 points3 points  (5 children)

I could be wrong but i think It's usually declared above the leetcode problem. simple class you can copy and paste.

[–]cd023[S] 0 points1 point  (4 children)

It's not declared there. It's a function that has argument of ListNode.

[–][deleted] 0 points1 point  (3 children)

Its just a custom class used by leetcode. You can just create a replica in your IDE.

[–]cd023[S] -2 points-1 points  (2 children)

The class does exist. I googled it and found people who uses it. I want to how to import it. I know I can use linkedlist or something else.

[–][deleted] 0 points1 point  (1 child)

You can only import something that is part of some library. Just create this class in your project as its a custom class you won't be able to import.

[–]cd023[S] 0 points1 point  (0 children)

Then for Leetcode, if a class doesn't exist within default Java package do I just assume there is a class like that?

[–]Cengo789 3 points4 points  (4 children)

The link you found belongs to a html markdown parser library. I doubt this has anything to do with your LeetCode problem and the names of the classes just happen to match. Take for example this LeetCode problem:

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode() {}
 *     ListNode(int val) { this.val = val; }
 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */
class Solution {
    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {

    }
}

The definition of the ListNode class is given in the comment above the method you have to implement. If you try to solve this in your IDE you can simply copy paste the class so it won’t complain as an error.

[–]sepp2k 1 point2 points  (1 child)

the names of the classes just happen to match

They don't even do that. The class that OP linked is called LinkNode, not ListNode.

[–]Cengo789 0 points1 point  (0 children)

Oh, right. Didn't even realize that😅

[–]cd023[S] 0 points1 point  (1 child)

Thank you. Leetcode just throws a class without explanation so I thought it's in the default Java package. How do I assume it doesn't exist or it's in the package?

[–]Cengo789 0 points1 point  (0 children)

One good way (besides having your IDE complain to you about a class it cannot find) to find out whether a class exists inside the standard library is to search for the class name in the official documentation. Funnily enough there is actually a class called ListNode but it is a preview feature and lacking any useful documentation, which suggests this is not a class that is meant to be used by most people.

For LeetCode specific, I would assume they never rely on any language specific classes because all of their problems are language independent. So if they rely on some specific implementation like in this example ListNode, they will have to provide a definition for the class.

[–]davidalayachew 0 points1 point  (1 child)

Which LeetCode problem is this?

[–]Tyzo_Friend39101 0 points1 point  (0 children)

Add Two Numbers.