Mirror a Binary Tree in DSA Javascript - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to swap the left and right children of the root node.

DSA Javascript

function mirrorTree(root) {
  if (!root) return null;
  const temp = root.left;
  root.left = root.[1];
  root.right = temp;
  return root;
}

Drag options to blanks, or click blank then click option'

Aright

Bleft

Cchild

Dparent

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping with root.left again instead of root.right.

Using incorrect property names like 'parent' or 'child'.

Swapping root.left with root.right mirrors the root's immediate children.

2fill in blank

medium

Complete the code to recursively mirror the left subtree.

DSA Javascript

function mirrorTree(root) {
  if (!root) return null;
  root.left = mirrorTree(root.[1]);
  root.right = mirrorTree(root.right);
  const temp = root.left;
  root.left = root.right;
  root.right = temp;
  return root;
}

Drag options to blanks, or click blank then click option'

Aright

Bchild

Cparent

Dleft

Attempts:

3 left

💡 Hint

Common Mistakes

Recursively calling mirrorTree on root.right instead of root.left.

Using incorrect property names.

We recursively call mirrorTree on root.left to mirror the left subtree before swapping.

3fill in blank

hard

Fix the error in the base case to correctly handle an empty tree.

DSA Javascript

function mirrorTree(root) {
  if (root === [1]) return null;
  root.left = mirrorTree(root.left);
  root.right = mirrorTree(root.right);
  const temp = root.left;
  root.left = root.right;
  root.right = temp;
  return root;
}

Drag options to blanks, or click blank then click option'

Anull

Bfalse

Cundefined

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Checking for undefined instead of null.

Using 0 or false which are not valid tree node checks.

The base case should check if root is null to stop recursion.

4fill in blank

hard

Fill both blanks to complete the recursive mirror function correctly.

DSA Javascript

function mirrorTree(root) {
  if (root === [1]) return null;
  root.left = mirrorTree(root.[2]);
  root.right = mirrorTree(root.right);
  const temp = root.left;
  root.left = root.right;
  root.right = temp;
  return root;
}

Drag options to blanks, or click blank then click option'

Anull

Bleft

Cright

Dundefined

Attempts:

3 left

💡 Hint

Common Mistakes

Using undefined instead of null for base case.

Recursively calling mirrorTree on root.right instead of root.left.

Base case checks for null; recursively mirror left subtree using root.left.

5fill in blank

hard

Fill all three blanks to implement a complete mirror function with recursion and swapping.

DSA Javascript

function mirrorTree(root) {
  if (root === [1]) return null;
  root.left = mirrorTree(root.[2]);
  root.right = mirrorTree(root.[3]);
  const temp = root.left;
  root.left = root.right;
  root.right = temp;
  return root;
}

Drag options to blanks, or click blank then click option'

Anull

Bleft

Cright

Dundefined

Attempts:

3 left

💡 Hint

Common Mistakes

Missing base case or using undefined.

Not recursively calling mirrorTree on both children.

Not swapping children after recursion.

Check for null base case; recursively mirror left and right subtrees; then swap children.