Check if Binary Tree is Balanced in DSA Javascript - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does it mean for a binary tree to be balanced?

A binary tree is balanced if for every node, the height difference between its left and right subtrees is at most 1.

beginner

What is the main idea behind checking if a binary tree is balanced?

We check the height of left and right subtrees for every node and ensure their difference is not more than 1.

intermediate

Why is it efficient to check balance and height in the same recursion?

Because it avoids repeated height calculations, reducing time complexity from O(n²) to O(n).

intermediate

What does a return value of -1 usually indicate in a balanced tree check function?

It indicates that the subtree is not balanced, so the whole tree is unbalanced.

beginner

In JavaScript, how can you represent a binary tree node?

A node can be an object with properties: value, left (child), and right (child). Example: { value: 5, left: null, right: null }

What is the maximum allowed height difference between left and right subtrees for a node to be balanced?

A 0

B No limit

C 2

D 1

A balanced binary tree requires the height difference to be at most 1.

Which approach is best to check if a binary tree is balanced efficiently?

A Use a single recursive function that returns height or -1 if unbalanced

B Calculate height separately for each node multiple times

C Traverse the tree level by level only

D Count the total number of nodes

Using one recursive function that returns height or -1 avoids repeated calculations.

If a subtree is unbalanced, what should the recursive function return to stop further checks?

A 0

B null

C -1

D Infinity

Returning -1 signals unbalanced subtree and stops further recursion.

What is the time complexity of the efficient balanced tree check algorithm?

A O(n²)

B O(n)

C O(n log n)

D O(log n)

The efficient algorithm visits each node once, so time complexity is O(n).

In JavaScript, which property is NOT typically part of a binary tree node?

A parent

B left

C right

D value

Parent is not always stored; usually nodes have value, left, and right.

Explain how to check if a binary tree is balanced using recursion.

Think about returning height or a special value to indicate imbalance.

Describe why checking balance and height in one recursive function is better than separate calls.

Consider how many times each node is visited.