Validate string valid BST
Last updated: July 15, 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 is defined as a tree where 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 value: true if the tree is a valid BST, and false otherwise.
Oracle
July 15, 2025281
12
4,114 solved
Given a binary tree, implement a function to determine if the tree is a valid binary search tree (BST). A valid BST is defined as a tree where 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 value: true if the tree is a valid BST, and false otherwise.
Coding interviews at Oracle 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
- Identify the correct data structure and algorithm for the problem
- Write clean, bug-free code with proper variable naming
- Analyze time and space complexity correctly
- Handle basic edge cases (empty input, single element)
- Communicate your thought process while coding
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)?
- How would your solution change if the input was sorted?
- 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 need to ensure that for every node, all values in its left subtree are less than the node's value, and all values in its right sub...
Approach
- Define a recursive function that takes a node, along with its permissible minimum and maximum values.
- If the current node is null, return true as an empty subtree is a valid BST.
- Check if...
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