Mirror a Binary Tree in DSA Typescript - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

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

DSA Typescript

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

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

Aroot.left

Broot.right

Cnull

Droot

Attempts:

3 left

💡 Hint

Common Mistakes

Assigning root.left to itself instead of root.right.

Assigning null instead of the right child.

We swap the left child with the right child, so root.left becomes root.right.

2fill in blank

medium

Complete the code to recursively mirror the left subtree.

DSA Typescript

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

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AmirrorTree(root.right)

Broot.right

Croot.left

DmirrorTree(root.left)

Attempts:

3 left

💡 Hint

Common Mistakes

Calling mirrorTree on root.left instead of root.right.

Assigning root.left directly without recursion.

We need to recursively mirror the right subtree, so we call mirrorTree(root.right) for the left child after swapping.

3fill in blank

hard

Fix the error in the recursive calls to mirror both subtrees correctly.

DSA Typescript

function mirrorTree(root: TreeNode | null): TreeNode | null {
  if (root === null) return null;
  const leftMirrored = mirrorTree(root.left);
  const rightMirrored = [1];
  root.left = rightMirrored;
  root.right = leftMirrored;
  return root;
}

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

AmirrorTree(root.right)

BmirrorTree(root.left)

Croot.left

Droot.right

Attempts:

3 left

💡 Hint

Common Mistakes

Calling mirrorTree on root.left twice.

Assigning root.left or root.right directly without recursion.

To mirror the tree, we recursively call mirrorTree on the right child for rightMirrored.

4fill in blank

hard

Fill both blanks to complete the recursive mirror function that swaps children after mirroring.

DSA Typescript

function mirrorTree(root: TreeNode | null): TreeNode | null {
  if (root === null) return null;
  const leftMirrored = [1];
  const rightMirrored = [2];
  root.left = rightMirrored;
  root.right = leftMirrored;
  return root;
}

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

AmirrorTree(root.left)

BmirrorTree(root.right)

Croot.left

Droot.right

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping without recursion.

Calling mirrorTree on the same child twice.

We recursively mirror the left and right subtrees before swapping them.

5fill in blank

hard

Fill both blanks to create a one-liner recursive mirror function using destructuring assignment.

DSA Typescript

function mirrorTree(root: TreeNode | null): TreeNode | null {
  if (root === null) return null;
  [root.left, root.right] = [[1], [2]];
  return root;
}

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

AmirrorTree(root.right)

BmirrorTree(root.left)

Croot.left

Droot.right

Attempts:

3 left

💡 Hint

Common Mistakes

Not swapping the children correctly.

Using non-recursive values in the assignment.

We assign root.left to the mirrored right subtree and root.right to the mirrored left subtree using recursion.