Validate binary tree symmetric
Last updated: October 23, 2025
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.
Cloudflare
October 23, 2025112
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3,010 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.
This coding problem is frequently asked during Technical Screen at Cloudflare. The interviewer is testing your ability to translate a problem into clean, working code while discussing time and space complexity. Cloudflare 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
- Can you solve this iteratively instead of recursively (or vice versa)?
- What happens if the input contains duplicates?
- How would you parallelize this solution?
- What is the worst-case input for your solution?
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Problem Analysis
To determine if a binary tree is symmetric around its center, we need to compare the left and right subtrees of the tree. This problem can be effectively solved using a recursive approach, which resem...
Approach
The approach involves a helper function that recursively checks whether two trees are mirror images of each other. Here are the steps:
- Base Case: If both nodes are null, return true (both subtr...
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