Count Total Nodes in Binary Tree in DSA Typescript - Build from Scratch

Count Total Nodes in Binary Tree

📖 Scenario: You are working with a simple binary tree structure used in many applications like organizing data or representing decisions. Your task is to count how many nodes are in this tree.

🎯 Goal: Build a TypeScript program that creates a binary tree, sets up a counter, counts all nodes in the tree using a function, and prints the total count.

📋 What You'll Learn

Create a binary tree using the given TreeNode class

Create a variable count to hold the total number of nodes

Write a recursive function countNodes that counts nodes in the tree

Print the total number of nodes using console.log

💡 Why This Matters

🌍 Real World

Counting nodes in a binary tree is useful in many areas like file systems, decision trees, and organizing data hierarchically.

💼 Career

Understanding tree traversal and counting nodes is a fundamental skill for software developers working with data structures, algorithms, and system design.

1

Create the binary tree

Create the binary tree nodes using the TreeNode class exactly as shown: root node with value 1, left child with value 2, and right child with value 3. Assign the root node to a variable called root.

DSA Typescript

class TreeNode {
    val: number;
    left: TreeNode | null;
    right: TreeNode | null;
    constructor(val: number, left: TreeNode | null = null, right: TreeNode | null = null) {
        this.val = val;
        this.left = left;
        this.right = right;
    }
}

// Create the binary tree nodes and assign to root
// Your code here

Hint

Use the new TreeNode(value, left, right) constructor to create nodes. The root has value 1, left child 2, and right child 3.

2

Create a count variable

Create a variable called count and set it to 0. This will hold the total number of nodes counted.

DSA Typescript

class TreeNode {
    val: number;
    left: TreeNode | null;
    right: TreeNode | null;
    constructor(val: number, left: TreeNode | null = null, right: TreeNode | null = null) {
        this.val = val;
        this.left = left;
        this.right = right;
    }
}

const root = new TreeNode(1, new TreeNode(2), new TreeNode(3));

// Create a variable count and set it to 0
// Your code here

Hint

Use let count = 0; to create the variable.

3

Write the recursive function to count nodes

Write a recursive function called countNodes that takes a TreeNode | null parameter called node. If node is not null, increase count by 1, then call countNodes on node.left and node.right.

DSA Typescript

class TreeNode {
    val: number;
    left: TreeNode | null;
    right: TreeNode | null;
    constructor(val: number, left: TreeNode | null = null, right: TreeNode | null = null) {
        this.val = val;
        this.left = left;
        this.right = right;
    }
}

const root = new TreeNode(1, new TreeNode(2), new TreeNode(3));

let count = 0;

// Write the recursive function countNodes
// Your code here

Hint

Use a function with a base check for null. Increase count by 1 for each node, then call the function on left and right children.

4

Call the function and print the total count

Call the function countNodes with the variable root as argument. Then print the value of count using console.log(count).

DSA Typescript

class TreeNode {
    val: number;
    left: TreeNode | null;
    right: TreeNode | null;
    constructor(val: number, left: TreeNode | null = null, right: TreeNode | null = null) {
        this.val = val;
        this.left = left;
        this.right = right;
    }
}

const root = new TreeNode(1, new TreeNode(2), new TreeNode(3));

let count = 0;

function countNodes(node: TreeNode | null): void {
    if (node !== null) {
        count += 1;
        countNodes(node.left);
        countNodes(node.right);
    }
}

// Call countNodes with root and print count
// Your code here

Hint

Call countNodes(root); then print count with console.log(count);.