Check if Binary Tree is Balanced in DSA Typescript - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to return the height of the tree or -1 if unbalanced.

DSA Typescript

function checkHeight(node: TreeNode | null): number {
  if (node === null) return [1];
  // rest of code omitted for brevity
}

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

A0

B-1

Cnull

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Returning -1 for null node height causes incorrect balance checks.

When the node is null, height is 0 because empty tree has height zero.

2fill in blank

medium

Complete the code to check if the left subtree is balanced.

DSA Typescript

const leftHeight = checkHeight(node.left);
if (leftHeight === [1]) return -1;

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

A0

Bnull

C1

D-1

Attempts:

3 left

💡 Hint

Common Mistakes

Checking for 0 instead of -1 causes missing unbalanced detection.

If left subtree is unbalanced, checkHeight returns -1, so we propagate -1 upwards.

3fill in blank

hard

Fix the error in the balance difference check.

DSA Typescript

if (Math.abs(leftHeight - rightHeight) > [1]) return -1;

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

A1

B0

C2

D-1

Attempts:

3 left

💡 Hint

Common Mistakes

Using 0 or 2 causes incorrect balance detection.

The tree is unbalanced if height difference is more than 1.

4fill in blank

hard

Fill both blanks to return the height of the current node.

DSA Typescript

return Math.max([1], [2]) + 1;

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

AleftHeight

BrightHeight

Cnode.left

Dnode.right

Attempts:

3 left

💡 Hint

Common Mistakes

Using node.left or node.right instead of their heights causes errors.

The height of current node is max of left and right subtree heights plus one.

5fill in blank

hard

Fill all three blanks to complete the isBalanced function.

DSA Typescript

function isBalanced(root: TreeNode | null): boolean {
  return checkHeight([1]) !== [2];
}

function checkHeight(node: TreeNode | null): number {
  if (node === null) return [3];
  const leftHeight = checkHeight(node.left);
  if (leftHeight === -1) return -1;
  const rightHeight = checkHeight(node.right);
  if (rightHeight === -1) return -1;
  if (Math.abs(leftHeight - rightHeight) > 1) return -1;
  return Math.max(leftHeight, rightHeight) + 1;
}

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

Aroot

B-1

C0

Dnode

Attempts:

3 left

💡 Hint

Common Mistakes

Returning true if checkHeight returns -1 causes wrong result.

Returning -1 for null node height causes errors.

Call checkHeight on root, return true if result is not -1, and height of null node is 0.