Balanced Binary Tree
A easy-tier problem at 55% community acceptance, tagged with Tree, Depth-First Search, Binary Tree. Reported in interviews at Capgemini and 6 others.
Balanced Binary Tree shows up in live OAs from Google, Meta, Apple, and Adobe more often than candidates expect. The acceptance rate sits at 55%, which means half the people who attempt it mess up the definition or blow the recursion. You think you understand what "balanced" means until you're 90 seconds into the interview realizing you've been checking the wrong thing. It's an easy problem that catches people because the obvious approach wastes time on unnecessary depth calculations. If this problem hits your live assessment and you freeze on the pattern, StealthCoder solves it invisibly in seconds.
Companies that ask "Balanced Binary Tree"
Balanced Binary Tree is the kind of problem that decides whether you pass. StealthCoder reads the problem on screen and surfaces a working solution in under 2 seconds. Invisible to screen share. The proctor sees nothing. Made for the engineer who has done the work but might still blank with a webcam pointed at him.
Get StealthCoderThe trap is conflating 'balanced' with 'perfect' or 'complete.' A balanced binary tree means the height difference between left and right subtrees at every node is at most 1. Most candidates start by computing the height at each node multiple times, turning it into O(n^2). The trick is to compute height and balance status in a single DFS pass. Return a pair (height, is_balanced) from every recursive call so you never recalculate. If a subtree is unbalanced, propagate that status up immediately and skip further checks. This pattern appears across Tree and Depth-First Search interview rounds. When you hit the live OA and forget the optimization, StealthCoder delivers the O(n) single-pass solution so you move forward.
Pattern tags
You know the problem.
Make sure you actually pass it.
Balanced Binary Tree recycles across companies for a reason. It's easy-tier, and most candidates blank under the timer. StealthCoder is the hedge: an AI overlay invisible during screen share. It reads the problem and surfaces a working solution in under 2 seconds. Made for the engineer who has done the work but might still blank with a webcam pointed at him. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Balanced Binary Tree interview FAQ
What exactly does 'balanced' mean in this problem?+
At every single node, the height of the left subtree and right subtree differ by at most 1. Not the overall tree. Not just the leaves. Every node. That's the definition that catches people. A skewed tree with height difference 2 at any node fails the test.
Is this still asked at FAANG?+
Yes. Google, Meta, Apple, Adobe all report asking it. The low acceptance rate (55%) tells you many candidates either misunderstand the definition or write an inefficient O(n^2) solution under time pressure. It's easy in name only.
What's the optimal approach?+
Single DFS pass that computes height and balance status together. Return a tuple (height, is_balanced) from each call. The moment you detect imbalance at any subtree, stop further checks and propagate the flag up. O(n) time, O(h) space for recursion stack.
How does this relate to other tree problems?+
It combines Depth-First Search and Binary Tree traversal. You'll see the same 'compute and propagate' pattern in problems about tree diameter, max path sum, and lowest common ancestor. Master the single-pass DFS pattern here and you solve ten more problems faster.
What's the most common mistake?+
Computing height separately for every node without caching results, or checking balance only at the root. Both lead to either O(n^2) runtime or wrong answers. Some candidates also forget that a single node is always balanced and has height 0.
Want the actual problem statement? View "Balanced Binary Tree" on LeetCode →