Validate binary tree complete
Last updated: August 20, 2025
Quick Overview
Given a binary tree, write a function to determine if it is a complete binary tree. A complete binary tree is defined as every level, except possibly the last, being completely filled, and all nodes are as far left as possible. The function should return a boolean value indicating whether the tree meets this criterion.
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Given a binary tree, write a function to determine if it is a complete binary tree. A complete binary tree is defined as every level, except possibly the last, being completely filled, and all nodes are as far left as possible. The function should return a boolean value indicating whether the tree meets this criterion.
This coding problem is frequently asked during Technical Screen at Google. The interviewer is testing your ability to translate a problem into clean, working code while discussing time and space complexity. Google expects candidates to write production-quality code, not just solve the puzzle.
What the Interviewer Expects
- Recognize the underlying problem pattern (sliding window, two pointers, BFS/DFS, etc.)
- Discuss multiple approaches and trade-offs before coding
- Implement an optimal solution with clean, production-quality code
- Handle all edge cases including boundary conditions and invalid input
- Optimize both time and space complexity with clear justification
- Test your solution systematically with well-chosen examples
Key Topics to Cover
How to Approach This
- Clarify input constraints and edge cases before writing code.
- Walk through your approach verbally and confirm with the interviewer before coding.
- Start with a brute force solution, then optimize. Mention time and space complexity.
- Test your solution with examples, including edge cases like empty input or duplicates.
- Consider common patterns: sliding window, two pointers, hash map, BFS/DFS, dynamic programming.
Possible Follow-up Questions
- What if the input doesn't fit in memory?
- Can you solve this in a single pass?
- How would you parallelize this solution?
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Practice DSA ProblemsSample Answer
Problem Analysis
To determine if a binary tree is complete, we can utilize a breadth-first search (BFS) approach. A complete binary tree has the following properties: every level, except possibly the last, is fully fi...
Approach
- Initialize a queue and start by adding the root node.
- Use a flag
endto indicate if we have encountered a node that is not a full child (i.e., a node that is not fully populated). - While...
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