Find kth largest element in binary tree
Last updated: February 25, 2026
Quick Overview
Given a binary tree, write a function to find the kth largest element in the tree. The function should take the root of the binary tree and an integer k as input, and return the kth largest element as output. You may assume that k is always valid, and there are no duplicate elements in the tree.
Airbnb
February 25, 2026117
10
3,282 solved
Given a binary tree, write a function to find the kth largest element in the tree. The function should take the root of the binary tree and an integer k as input, and return the kth largest element as output. You may assume that k is always valid, and there are no duplicate elements in the tree.
Airbnb uses this problem in the Onsite to evaluate your algorithmic thinking. They expect you to discuss multiple approaches, analyze trade-offs between them, and implement the optimal solution with clean, readable code.
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
- How would you modify your solution to handle streaming input?
- Can you optimize the space complexity of your solution?
- Can you solve this in a single pass?
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Practice DSA ProblemsSample Answer
Problem Analysis
To find the kth largest element in a binary tree, we can utilize an in-order traversal approach because it allows us to visit the nodes in a sorted manner for a Binary Search Tree (BST). However, ...
Approach
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Traverse the Tree: We will perform a DFS to collect all the node values in a list. For example, given a tree structure:
5/
3 8 / \
2 4 9The...
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