getParent() is not working!

Question about the task

Build a tree (part 4)

Java Collections, Level 1, Lesson 15

Under discussion

Any hint's!? Tk you!

Every tree starts with a root, so don't forget to add an Entry<String> field called root with the default access modifier to the CustomTree class.

Initialize it in the CustomTree constructor. It's name (elementName) isn't important.

Now that we've built the tree's foundation, it's time for you to do a little work on your own.

Recall what our tree should look like.

The nodes of the tree should be like those in the picture:

Now we need to write methods that will allow us to create and perform operations on that tree structure.

You need to:
1) override the add(String s) method, which adds tree nodes; it takes a node name as an argument (elementName) and searches left to right for a place to insert it.
2) override the size() method so it returns the current number of nodes in the tree.
3) implement the getParent(String s) method so it returns the name of the parent of the tree node passed as an argument.

You can create methods and fields not listed in the task, if necessary.

Requirements:

There must be an Entry field called root in the CustomTree.Entry class.
Override the add(String s) and size() methods in the CustomTree class.
After using the add method to add N nodes to the tree, the size method must return N.
The getParent method must return the name of the parent of any node in the tree.

package com.codegym.task.task20.task2028; import java.util.List; public class Solution { public static void main(String[] args) { List<String> list = new CustomTree(); for (int i = 1; i < 16; i++) { list.add(String.valueOf(i)); } System.out.println("The list size is " + list.size()); System.out.println("The expected parent is 3. The actual parent is " + ((CustomTree) list).getParent("8")); System.out.println("The expected parent is null. The actual parent is " + ((CustomTree) list).getParent("20")); } }

Comments (3)

Popular
New
Old

You must be signed in to leave a comment

Lisa L

Level 47 , Nuremberg, Germany

23 March 2022, 05:44

Looks OK. In theory, just as you do with adding elements, you traverse the tree level order and, once you find a match, you break (implement that or return right inside the loop) and return the found value. If you do not find a match, then usually you return null (instead of creating an object with a made up value).

Angel Stefan

Level 23 , Sibiu, Romania

23 March 2022, 22:32

I made this so it can return parent = x.parent.elementName; || parent = null; but is not working... So, it s "simple", or x.parent.elementName is not the parent of x? public String getParent(String s){ String parent = null; for(Entry<String> x : tree){ if(x.elementName.equals(s)){ //when String x = String s parent = x.parent.elementName; // parent = name of parent of x break; } } return parent; }

Lisa L

Level 47 , Nuremberg, Germany

24 March 2022, 06:32

it should be that simple. However there is still a little problem in your code (not related to the getParent method). You probably may find it, if you thoroughly debug your code. I wrote a toString method for your tree. It is not dependent on the list. It is more the pure doctrine, just using the root element to iterate (as the list also would do) level order through the tree. To do this is necessary, otherwise you won't see the issue.

@Override
public String toString() {
    StringBuilder sb = new StringBuilder("CustomTree{");
    Entry<String> current;
    Queue<Entry<String>> buffer = new LinkedList<>();
    buffer.offer(root);
    while (!buffer.isEmpty()) {
        current = buffer.poll();
        sb.append(current.elementName).append(", ");

        if (current.leftChild != null)
            buffer.offer(current.leftChild);
        if (current.rightChild != null)
            buffer.offer(current.rightChild);
    }
    sb.append("}");

    return sb.toString();
}

As you can see, there are faaaar to many elements in your tree. Here the toString method based just on the list. Try that one, too. It shows you a supposedly correct result.

@Override
public String toString() {
    StringBuilder sb = new StringBuilder("CustomTree{");
    for (Entry<String> element : tree) {
        sb.append(element.elementName).append(", ");
    }
    return sb.toString();
}

If you need more hints or named the problem...