Validate binary tree complete
Last updated: July 6, 2025
Quick Overview
Given a binary tree, implement 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. Your function should return a boolean value indicating whether the tree meets this criterion.
MongoDB
July 6, 20255
16
3,747 solved
Given a binary tree, implement 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. Your function should return a boolean value indicating whether the tree meets this criterion.
Coding interviews at MongoDB focus on problem-solving approach as much as the final solution. The interviewer wants to see you break down the problem, consider edge cases, and optimize iteratively. Communication throughout the process is key.
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 happens if the input contains duplicates?
- How would your solution change if the input was sorted?
- Can you solve this iteratively instead of recursively (or vice versa)?
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Practice DSA ProblemsSample Answer
Problem Analysis
To determine if a binary tree is a complete binary tree, we can leverage the properties of level-order traversal using a queue (BFS approach). A complete binary tree must satisfy the following conditi...
Approach
- Initialize a queue to facilitate level-order traversal. Start by enqueuing the root node.
- While the queue is not empty, dequeue nodes one by one:
- For each node, check if it is null....
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