Related Coding / DSA
Cheapest Route Within a Stop Limit
Given one-way routes between cities each with a cost, find the cheapest total cost from a source city to a destination city using at most k intermediate stops.
1. Problem Statement
You are given the root of a binary tree. Determine whether it is a valid binary search tree.
2. Live Coding Format
Work in the provided coding workspace while explaining your decisions to the live interviewer. Validation may use inline tests, examples, comments, or a verbal walkthrough.
3. Key Focus Areas
- 1Problem clarification and contract
- 2Approach exploration and optimality
- 3Think-aloud communication and pacing
- 4Implementation correctness
- 5Code quality and language fluency
- 6Tests and dry run
- 7Debugging and self-correction
- 8Complexity analysis
- 9Follow-up performance
4. What Strong Candidates Should Demonstrate
- Clarify the strictness of the ordering property and duplicate-value policy before coding.
- State the ordering property precisely and implement a correct linear-time check.
- Think aloud while implementing readable, correct code.
- Validate with explicit expected outputs and a top-to-bottom dry run.
- Analyze time and space complexity and handle a bounded follow-up modification.
Want interactive feedback?
Practice this problem in the live coding workspace while the interviewer probes your clarification, implementation, trade-offs, and validation.
Continue to DashboardCore Concepts
Hidden because they name the technique, which a real interviewer would not tell you.
Show core concepts
TreesBinary Search TreesRecursionComplexity Analysis
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Minimum Coins to Reach an Amount
Given a set of coin denominations and a target amount, find the minimum number of coins (with unlimited supply of each denomination) needed to make exactly that amount, or report it is impossible.
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Minimum Time for Contamination to Spread
Given a grid where each cell is empty, clean, or already contaminated, find the minimum time for all clean cells to become contaminated, spreading one step per unit time to adjacent cells, or report it is impossible.
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Determine a Valid Course Completion Order
Given a number of courses and a list of prerequisite pairs, determine a valid order to complete all courses, or report that no valid order exists.