Validate grid valid BST
Last updated: February 18, 2026
Quick Overview
Given a binary tree represented as a grid, implement a function to validate whether it is a valid binary search tree (BST). A valid BST must satisfy the property that for any given 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 grid represents a valid BST.
Notion
February 18, 20261
11
1,786 solved
Given a binary tree represented as a grid, implement a function to validate whether it is a valid binary search tree (BST). A valid BST must satisfy the property that for any given 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 grid represents a valid BST.
This coding problem is frequently asked during Take-home Project at Notion. The interviewer is testing your ability to translate a problem into clean, working code while discussing time and space complexity. Notion 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
- How would your solution change if the input was sorted?
- How would you modify your solution to handle streaming input?
- How would you parallelize this solution?
- Can you optimize the space complexity of your solution?
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Practice DSA ProblemsSample Answer
Problem Analysis
The problem requires us to validate whether a binary tree represented as a grid is a valid binary search tree (BST). The properties of a BST state that for any node, all values in the left subtree mus...
Approach
- Initialize Recursive Function: Define a recursive function that takes the current node's value, and minimum and maximum bounds as parameters.
- Base Case: If the current position in the g...
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