Height of Binary Tree in DSA Typescript - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to return the height of a binary tree.

DSA Typescript

function height(root: TreeNode | null): number {
  if (root === null) {
    return [1];
  }
  return 1 + Math.max(height(root.left), height(root.right));
}

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

Anull

B1

C0

D-1

Attempts:

3 left

💡 Hint

Common Mistakes

Returning 1 instead of 0 for a null node.

Returning null which causes errors.

The height of an empty tree is 0, so we return 0 when the node is null.

2fill in blank

medium

Complete the code to calculate the height by comparing left and right subtree heights.

DSA Typescript

return 1 + Math.[1](height(root.left), height(root.right));

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

Amax

Bmin

Csum

Dabs

Attempts:

3 left

💡 Hint

Common Mistakes

Using min instead of max which gives wrong height.

Using sum which overcounts height.

The height of a binary tree is 1 plus the maximum height of its left and right subtrees.

3fill in blank

hard

Fix the error in the base case to correctly handle empty nodes.

DSA Typescript

if (root [1] null) {
  return 0;
}

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

A==

B!==

C!=

D===

Attempts:

3 left

💡 Hint

Common Mistakes

Using == which can cause unexpected behavior.

Using != or !== which check for inequality.

Use strict equality (===) to check if root is exactly null for type safety.

4fill in blank

hard

Fill both blanks to complete the recursive height calculation.

DSA Typescript

const leftHeight = height(root.[1]);
const rightHeight = height(root.[2]);
return 1 + Math.max(leftHeight, rightHeight);

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

Aleft

Bright

Cparent

Dchild

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'parent' or 'child' which are not valid properties.

Mixing left and right properties.

We calculate height of left and right subtrees by accessing root.left and root.right.

5fill in blank

hard

Fill all three blanks to create a function that returns the height of a binary tree.

DSA Typescript

function height([1]: TreeNode | null): number {
  if ([2] === null) {
    return [3];
  }
  return 1 + Math.max(height([2].left), height([2].right));
}

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

Aroot

C0

Dnode

Attempts:

3 left

💡 Hint

Common Mistakes

Using different variable names inconsistently.

Returning 1 instead of 0 for null nodes.

The function parameter is named 'root'. We check if 'root' is null and return 0 if yes.

Practice

1. What does the height of a binary tree represent?

easy

A. The number of edges on the longest path from root to a leaf

B. The total number of nodes in the tree

C. The number of leaf nodes in the tree

D. The number of nodes at the root level

Solution

1. Step 1: Understand the definition of height in a binary tree

   The height is the longest path from the root node down to the farthest leaf node, counted by edges.

2. Step 2: Differentiate height from other tree properties

   Number of nodes or leaf nodes are different concepts; height specifically counts edges on the longest path.

3. Final Answer:

   The number of edges on the longest path from root to a leaf -> Option A

4. Quick Check:

   Height = longest root-to-leaf edge count [OK]

Hint: Height counts edges, not nodes, on longest root-to-leaf path [OK]

Common Mistakes:

• Confusing height with total nodes count
• Counting nodes instead of edges for height
• Thinking height equals number of leaf nodes

2. Which TypeScript function signature correctly defines a recursive function to find the height of a binary tree node?

easy

A. function height(node: TreeNode | null): number

B. function height(node: number): number

C. function height(): void

D. function height(node: TreeNode): string

Solution

1. Step 1: Identify the correct parameter type for a tree node

   The function must accept a node or null (for empty subtree), so type is TreeNode | null.

2. Step 2: Confirm the return type is number

   The height is a numeric value, so the return type must be number.

3. Final Answer:

   function height(node: TreeNode | null): number -> Option A

4. Quick Check:

   Parameter: TreeNode|null, Return: number [OK]

Hint: Height function needs node or null input and returns number [OK]

Common Mistakes:

• Using wrong parameter type like number instead of node
• Returning void or string instead of number
• Missing null to handle empty subtree

3. What is the height of the following binary tree?

    1
   / \
  2   3
 / 
4  

Consider height as number of edges on longest path from root to leaf.

medium

A. 3

B. 4

C. 1

D. 2

Solution

1. Step 1: Identify all root-to-leaf paths and count edges

   Paths: 1->2->4 has 2 edges, 1->3 has 1 edge.

2. Step 2: Find the longest path edge count

   Longest path is 1->2->4 with 2 edges.

3. Final Answer:

   2 -> Option D

4. Quick Check:

   Longest path edges = 2 [OK]

Hint: Count edges, not nodes, on longest root-to-leaf path [OK]

Common Mistakes:

• Counting nodes instead of edges
• Choosing shorter path length
• Confusing height with tree depth

4. Identify the error in this TypeScript function to find binary tree height:

function height(node: TreeNode | null): number {
  if (!node) return 0;
  return Math.max(height(node.left), height(node.right));
}

medium

A. Returns 0 for null node instead of -1

B. Uses Math.min instead of Math.max

C. Missing +1 to count current node edge

D. Function should return void

Solution

1. Step 1: Analyze base case return value

   Returning 0 for null means empty subtree height is 0, which is acceptable if counting edges from nodes.

2. Step 2: Check recursive return statement

   Function returns max height of children but misses adding 1 for current edge from node to child.

3. Final Answer:

   Missing +1 to count current node edge -> Option C

4. Quick Check:

   Height = max child height + 1 edge [OK]

Hint: Add +1 after max to include current node edge [OK]

Common Mistakes:

• Forgetting to add 1 for current node edge
• Returning wrong base case value
• Using min instead of max for height

5. Given a binary tree where each node has a value, write a function to find the height of the tree but only counting nodes with even values. What is the height of this tree?

    2
   / \
  3   4
 /   / \
6   5   8

hard

A. 0

B. 2

C. 1

D. 3

Solution

1. Step 1: Identify nodes with even values and their connections

   Even nodes: 2 (root), 4 (right child), 6 (left-left child), 8 (right-right child). Paths counting only even nodes:
• 2 -> 4 -> 8 (edges = 2)
• 2 -> 3 (3 is odd, so path ends at 2)
• 2 -> 3 -> 6 (6 is even but 3 is odd, so path breaks at 3)

2. Step 2: Calculate height counting only edges between even nodes

   Longest path with even nodes is 2 -> 4 -> 8 with 2 edges.

3. Final Answer:

   2 -> Option B

4. Quick Check:

   Longest even-valued node path edges = 2 [OK]

Hint: Count edges only between even-valued nodes [OK]

Common Mistakes:

• Counting odd nodes in path
• Counting nodes instead of edges
• Ignoring breaks caused by odd nodes