Amplitude·Software Engineer·Technical Phone Screen·Intermediate

Intermediate

May 2026

Summary

Amplitude SWE interview with a tree validation problem that sounds straightforward but has enough moving parts to trip you up if you're not careful about how you structure your solution.

Questions Asked (1)

Given a forest of employee objects where each node can have sub-employees (direct reports), write a function that validates every employee in the hierarchy against a configurable set of rules. An employee is only considered valid if it passes all rules AND every one of its transitive reports does too. Discuss your data structure choices, how you'd organize the rule set, whether to short-circuit on first failure or collect all violations, and the time complexity.

Algorithms & Data StructuresTechnical Trade-offsSystem Design

Author's notes

I went straight for a recursive DFS and that part was fine.

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AI HintsAI Generated

Suggested Approach

Start by clarifying requirements and assumptions, then propose a recursive or iterative traversal of the employee forest, applying a configurable rule set to each node. Discuss trade-offs between short-circuiting and collecting all violations, and analyze time and space complexity. Finally, mention potential optimizations like memoization or parallel processing.

Pro tip: Demonstrate awareness of real-world constraints: ask whether the hierarchy is static or dynamic, and whether rules can be composed or prioritized. This shows you think beyond the algorithm and consider maintainability and scalability.

1. Clarify requirements and assumptions

Ask about the structure of employee objects, the nature of rules (e.g., pure functions, async), and whether the forest is static. Confirm if validation should return a boolean or detailed violations.

2. Choose data structures and traversal

Represent the forest as a list of root nodes with children pointers. Use DFS (recursive or iterative with stack) to traverse each tree, ensuring all transitive reports are visited.

3. Organize the rule set

Encapsulate rules as an array of predicate functions, each taking an employee and returning a violation or null. This allows easy configuration and composition.

4. Decide on short-circuit vs. collect all

Discuss trade-offs: short-circuiting is faster for boolean validation but loses detail; collecting all violations is useful for reporting but may be slower. Propose a configurable strategy.

5. Analyze complexity and optimizations

Time complexity is O(N * R) where N is number of employees and R is number of rules. Space complexity is O(H) for recursion stack (H = height). Mention memoization if subtrees are shared, or parallelization for large forests.

Key Points to Mention

Tree traversal: DFS vs. BFS, recursive vs. iterative, handling deep hierarchies to avoid stack overflow.
Rule set design: using higher-order functions, composability, and separation of concerns.
Short-circuiting vs. collecting all violations: impact on performance and usability.
Time complexity: O(N * R) where N is total employees and R is number of rules; space complexity O(H) for recursion.
Edge cases: empty forest, null children, cyclic references (if possible), and asynchronous rules.
Scalability: potential for parallel processing, memoization, or incremental validation.

AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.