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TreeNode Class & Manual Tree Creation

In this lesson, we will create a TreeNode class that will allow us to create a binary tree in JavaScript. We will create our tree manually for now by creating instances of the TreeNode class and assigning them to the left and right properties of other nodes. Later, we will create a BinaryTree class that will allow us to create a binary tree by passing in values.

I'm going to set this up as a challenge. If you just want to follow along without trying it yourself, that is absolutely fine. You know what a binary tree is and you know how to create a class. If you want to try it yourself, here are the instructions.

Instructions

Create a class called TreeNode. This will represent a node in the tree. It will have a value property and a left and right property that will point to the left and right child nodes respectively. They will be initialized to null when the node is created.

Then use that class to create the following binary tree:

Hints

  • The constructor will take a value parameter.
  • Initialize the left and right properties to null in the constructor.
  • Create an instance for each node in the tree and assign the appropriate values to the left and right properties.

Solutions

Click For Solution 
class TreeNode {
  constructor(value) {
    this.value = value;
    this.left = null;
    this.right = null;
  }
}

const a = new TreeNode('a');
const b = new TreeNode('b');
const c = new TreeNode('c');
const d = new TreeNode('d');
const e = new TreeNode('e');
const f = new TreeNode('f');

a.left = b;
a.right = c;
b.left = d;
b.right = e;
c.right = f;

Explanation

  • Create the TreeNode class with a constructor that takes a value parameter.
  • Initialize the left and right properties to null. This is because we don't know what the left and right children will be when we create the node. We will assign them later.
  • Create an instance of the TreeNode class for each node in the tree.
  • Assign the appropriate values to the left and right properties.

The code above implements exactly what we see in the diagram.