Mirror a Binary Tree in DSA Javascript - Build from Scratch

Mirror a Binary Tree

📖 Scenario: Imagine you have a family tree represented as a binary tree. You want to create a mirror image of this tree, flipping it left to right, like looking at it in a mirror.

🎯 Goal: You will build a program that creates a mirror of a given binary tree by swapping the left and right children of every node.

📋 What You'll Learn

Create a binary tree node class called TreeNode with value, left, and right properties

Create a sample binary tree with exact nodes and structure

Write a function called mirrorTree that mirrors the binary tree by swapping left and right children recursively

Print the tree nodes in level order after mirroring to show the mirrored structure

💡 Why This Matters

🌍 Real World

Mirroring binary trees is useful in graphics, image processing, and reversing hierarchical data structures.

💼 Career

Understanding tree manipulations like mirroring helps in coding interviews and software roles involving data structures.

1

Create the Binary Tree Node Class and Sample Tree

Create a class called TreeNode with a constructor that takes value and sets left and right to null. Then create the following tree structure by creating nodes and linking them:
1
/ \
2 3
/ \ \
4 5 6

DSA Javascript

// Your code here

Hint

Define the TreeNode class first. Then create the root node with value 1. Add left and right children as shown in the tree diagram.

2

Create a Helper Function to Print the Tree in Level Order

Create a function called printLevelOrder that takes the root node and prints the values of the tree nodes level by level separated by spaces. Use a queue to traverse the tree breadth-first.

DSA Javascript

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

const root = new TreeNode(1);
root.left = new TreeNode(2);
root.right = new TreeNode(3);
root.left.left = new TreeNode(4);
root.left.right = new TreeNode(5);
root.right.right = new TreeNode(6);

// Your code here

Hint

Use a queue array starting with the root. Remove the first node, print its value, then add its children to the queue. Repeat until queue is empty.

3

Write the Mirror Function to Swap Left and Right Children

Write a function called mirrorTree that takes a node and swaps its left and right children recursively for the entire tree.

DSA Javascript

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

const root = new TreeNode(1);
root.left = new TreeNode(2);
root.right = new TreeNode(3);
root.left.left = new TreeNode(4);
root.left.right = new TreeNode(5);
root.right.right = new TreeNode(6);

function printLevelOrder(root) {
  if (!root) return;
  const queue = [root];
  const result = [];
  while (queue.length > 0) {
    const node = queue.shift();
    result.push(node.value);
    if (node.left) queue.push(node.left);
    if (node.right) queue.push(node.right);
  }
  console.log(result.join(' '));
}

// Write the mirrorTree function below
// Your code here

Hint

Swap the left and right children of the current node. Then call mirrorTree recursively on the left and right children.

4

Print the Mirrored Tree

Call mirrorTree with the root node, then call printLevelOrder with the root node to print the mirrored tree nodes in level order.

DSA Javascript

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

const root = new TreeNode(1);
root.left = new TreeNode(2);
root.right = new TreeNode(3);
root.left.left = new TreeNode(4);
root.left.right = new TreeNode(5);
root.right.right = new TreeNode(6);

function printLevelOrder(root) {
  if (!root) return;
  const queue = [root];
  const result = [];
  while (queue.length > 0) {
    const node = queue.shift();
    result.push(node.value);
    if (node.left) queue.push(node.left);
    if (node.right) queue.push(node.right);
  }
  console.log(result.join(' '));
}

function mirrorTree(node) {
  if (!node) return;
  const temp = node.left;
  node.left = node.right;
  node.right = temp;
  mirrorTree(node.left);
  mirrorTree(node.right);
}

// Call mirrorTree and printLevelOrder below
// Your code here

Hint

Call mirrorTree(root) to mirror the tree, then printLevelOrder(root) to print the mirrored tree nodes.