Validate binary tree symmetric
Last updated: June 8, 2026
Quick Overview
Given a binary tree, write a function to determine if it is symmetric around its center. A binary tree is considered symmetric if the left subtree is a mirror reflection of the right subtree. The function should return a boolean value: true if the tree is symmetric, and false otherwise.
MongoDB
June 8, 202614
12
3,894 solved
Given a binary tree, write a function to determine if it is symmetric around its center. A binary tree is considered symmetric if the left subtree is a mirror reflection of the right subtree. The function should return a boolean value: true if the tree is symmetric, and false otherwise.
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 if the input doesn't fit in memory?
- Can you solve this iteratively instead of recursively (or vice versa)?
- Can you optimize the space complexity of your solution?
- Can you solve this in a single pass?
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Problem Analysis
To determine if a binary tree is symmetric, we can recognize that the problem can be approached using the recursive tree traversal pattern. Specifically, we will leverage a **DFS (Depth First Sear...
Approach
- Base Case: If the root is null, the tree is symmetric (return true). If only one of the subtrees is null, the tree is not symmetric (return false).
- Recursive Function: Create a helper fu...
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