Is Balanced Binary Tree easy or hard?

Balanced Binary Tree is categorized as an Easy problem on LeetCode. The challenge lies in recognizing that height calculation and balance checking should be combined into one DFS traversal to achieve the optimal O(n) solution.

How to solve Balanced Binary Tree in O(n)?

Use a post-order DFS that returns the height of each subtree while checking the balance condition. If a subtree is unbalanced, return a sentinel value such as -1 and propagate it upward. This avoids repeated height calculations and ensures every node is processed only once.

What is the best approach for Balanced Binary Tree?

The optimized recursive depth-first search approach is the best solution. It calculates subtree height and checks balance in the same traversal using post-order DFS. Each node is visited once, resulting in O(n) time complexity and O(h) space for the recursion stack.

What data structure is used in Balanced Binary Tree?

The problem uses a binary tree data structure. The algorithm typically relies on depth-first search recursion to compute subtree heights and verify the balance condition at every node.

What is the time complexity of Balanced Binary Tree?

The optimal algorithm runs in O(n) time because each node in the binary tree is visited exactly once during the DFS traversal. A naive approach that recomputes subtree heights at every node takes O(n^2) time in the worst case.

Balanced Binary Tree Python or Java solution approach?

Most Python and Java solutions implement a recursive DFS helper function that returns subtree height. If the height difference exceeds one, the function returns -1 to indicate imbalance. The main function checks whether the final result is -1 to determine if the tree is balanced.

Is Balanced Binary Tree asked at Google, Amazon, or Meta?

Balanced Binary Tree is a common interview problem at companies like Amazon, Google, and Meta because it tests recursion, tree traversal, and understanding of subtree properties. Variations of this problem also appear in system design discussions involving balanced tree structures.

Description Solution Video 13:11

110. Balanced Binary Tree

Easy59.2% acceptance9 companies

Given a binary tree, determine if it is height-balanced.

Example 1:

Input: root = [3,9,20,null,null,15,7]
Output: true

Example 2:

Input: root = [1,2,2,3,3,null,null,4,4]
Output: false

Example 3:

Input: root = []
Output: true

Constraints:

The number of nodes in the tree is in the range [0, 5000].
-10⁴ <= Node.val <= 10⁴

Asked at 9 companies

Viasat Anduril Microsoft Amazon Meta Bloomberg Visa

Google Apple

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13:11

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110. Balanced Binary Tree

Asked at 9 companies

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