Validate string valid BST
Last updated: August 18, 2025
Quick Overview
Given a binary tree, implement a function to determine if the tree is a valid binary search tree (BST). A valid BST must satisfy the property that for each node, all values in its left subtree are less than the node's value, and all values in its right subtree are greater. The function should return a boolean indicating whether the tree is a valid BST.
Splunk
August 18, 202518
13
1,138 solved
Given a binary tree, implement a function to determine if the tree is a valid binary search tree (BST). A valid BST must satisfy the property that for each node, all values in its left subtree are less than the node's value, and all values in its right subtree are greater. The function should return a boolean indicating whether the tree is a valid BST.
Splunk uses this problem in the Phone Screen 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
- Quickly identify the optimal approach and its theoretical basis
- Handle complex algorithm design with multiple interacting components
- Write concise, elegant code under time pressure
- Prove correctness of your approach and discuss alternative solutions
- Optimize beyond the obvious: discuss constant factor improvements
- Address follow-up variations and explain how the solution generalizes
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?
- How would you modify your solution to handle streaming input?
- How would you test this solution thoroughly?
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Problem Analysis
To determine if a binary tree is a valid Binary Search Tree (BST), we can utilize the properties of BSTs: for any given node, all values in the left subtree must be less than the node's value, and all...
Approach
The approach involves a depth-first traversal of the tree, while checking if each node's value falls within a specified range.
- Start with the root node and set its valid range as (-infinity, +inf...
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