Question

Adapt the provided program to recreate the following tree:

10 18 21 15

import java.util.ArrayList;
import java.util.List;

public class TreeNode<T>{
public T data = null;
private List<TreeNode> children = new ArrayList<>();
private TreeNode parent = null;

public TreeNode() {
}
  
public TreeNode(T data) {
this.data = data;
}

public TreeNode<T> addChild(TreeNode child) {
child.setParent(this);
this.children.add(child);
return child;
}

public TreeNode<T> addChild(T data) {
TreeNode<T> newChild = new TreeNode<>(data);
newChild.setParent(this);
children.add(newChild);
return newChild;
}

public void addChildren(List<TreeNode> children) {
for(TreeNode t : children) {
t.setParent(this);
}
this.children.addAll(children);
}

public List<TreeNode> getChildren() {
return children;
}

private void setParent(TreeNode parent) {
this.parent = parent;
}

public TreeNode getParent() {
return parent;
}
}

Answer 1

Here is the completed code for this problem. Comments are included, go through it, learn how things work and let me know if you have any doubts or if you need anything to change. If you are satisfied with the solution, please rate the answer. Thanks

Note: I have only added code to make the required tree that you mentioned without making any modifications to the existing code in TreeNode class. If you are looking to create a Binary search tree using TreeNode class, just let me know. I have done that before.

// TreeNode.java

import java.util.ArrayList;

import java.util.List;

public class TreeNode<T> {

      public T data = null;

      private List<TreeNode> children = new ArrayList<TreeNode>();

      private TreeNode parent = null;

      public TreeNode() {

      }

      public TreeNode(T data) {

            this.data = data;

      }

      public TreeNode<T> addChild(TreeNode child) {

            child.setParent(this);

            this.children.add(child);

            return child;

      }

      public TreeNode<T> addChild(T data) {

            TreeNode<T> newChild = new TreeNode<T>(data);

            newChild.setParent(this);

            children.add(newChild);

            return newChild;

      }

      public void addChildren(List<TreeNode> children) {

            for (TreeNode t : children) {

                  t.setParent(this);

            }

            this.children.addAll(children);

      }

      public List<TreeNode> getChildren() {

            return children;

      }

      private void setParent(TreeNode parent) {

            this.parent = parent;

      }

      public TreeNode getParent() {

            return parent;

      }

      // a simple method defined to print a tree recursively

      static <T> void printTree(TreeNode<T> node, String indent) {

            if (node != null) {

                  // printing data of node with indent spaces before it

                  System.out.println(indent + node.data);

                  // looping through each child of node

                  for (TreeNode<T> child : node.children) {

                        // calling recursive method to print child with one extra

                        // indentation level

                        printTree(child, indent + "   ");

                  }

            }

      }

      public static void main(String[] args) {

            // creating all the TreeNode objects needed

            TreeNode<Integer> root = new TreeNode<Integer>(10);

            TreeNode<Integer> child1 = new TreeNode<Integer>(6);

            TreeNode<Integer> child2 = new TreeNode<Integer>(18);

            TreeNode<Integer> child11 = new TreeNode<Integer>(4);

            TreeNode<Integer> child12 = new TreeNode<Integer>(8);

            TreeNode<Integer> child21 = new TreeNode<Integer>(15);

            TreeNode<Integer> child22 = new TreeNode<Integer>(21);

            // linking nodes

            root.addChild(child1);

            root.addChild(child2);

            child1.addChild(child11);

            child1.addChild(child12);

            child2.addChild(child21);

            child2.addChild(child22);

            // now root points to a tree that is mentioned in the question.

            // you can do whatever you need with the tree now. Im just printing the

            // tree.

           

            // printing the tree using the helper method defined

            printTree(root, "");

      }

}

/*OUTPUT*/

3 48 12 6