Validate graph valid BST
Last updated: December 24, 2025
Quick Overview
Determine if a given graph satisfies the valid BST property.
DoorDash
December 24, 20252
3
2,006 solved
Determine if a given graph satisfies the valid BST property.
This coding problem is frequently asked during Take-home Project at DoorDash. The interviewer is testing your ability to translate a problem into clean, working code while discussing time and space complexity. DoorDash 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 test this solution thoroughly?
- What happens if the input contains duplicates?
- Can you solve this in a single pass?
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Practice DSA ProblemsSample Answer
Problem Analysis
To determine if a given graph satisfies the properties of a valid Binary Search Tree (BST), we need to ensure that for every node in the graph, all values in the left subtree are less than the node's ...
Approach
- Define a recursive helper function that takes a node and the valid range for its value. The initial call will have the range set to negative infinity and positive infinity.
- For each node, check...
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