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Confluent·Software Engineer·Technical Phone Screen·Intermediate

IntermediateRejected
Apr 2026Remote

Summary

Interviewed for a software engineering role at Confluent and got a Trie problem I hadn't seen before. The interviewer was hard to communicate with and I didn't finish in time. Rejection came the next day.

Questions Asked (1)

Q1

Given a Function class with a name and a list of argument types, implement a register() method and a findMatches() method. findMatches() should return all registered functions whose argument type list starts with the given prefix sequence of types.

Algorithms & Data StructuresAPI & Integrations
Author's notes

I knew a Trie was the right structure pretty quickly but couldn't get the implementation clean under pressure.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the requirements: how functions are registered, the data structure for storage, and the expected performance for findMatches. Then, choose an efficient data structure like a trie or a sorted list with binary search to support prefix matching on argument type sequences. Implement register() to add functions and findMatches() to traverse the structure and collect all functions whose argument types start with the given prefix.

Pro tip: Mention that you would discuss trade-offs between different data structures (e.g., trie vs. sorted list) and consider edge cases like empty prefix or no matches, showing you think about robustness and scalability.

1. Clarify Requirements

Ask about the expected number of functions, frequency of findMatches calls, and whether the argument types are comparable or can be hashed. This determines the optimal data structure.

2. Choose Data Structure

Select a trie (prefix tree) where each node represents an argument type and stores functions ending at that node. Alternatively, use a sorted list of type sequences and binary search for the prefix range.

3. Implement register()

Insert the function into the chosen data structure. For a trie, traverse or create nodes for each argument type and append the function to the node's list. For a sorted list, insert while maintaining order.

4. Implement findMatches()

Traverse the data structure according to the prefix. For a trie, follow the prefix nodes and collect all functions in the subtree. For a sorted list, find the range of sequences that start with the prefix using binary search.

5. Analyze Complexity and Edge Cases

Discuss time and space complexity: trie gives O(P + K) for findMatches where P is prefix length and K is number of matches; sorted list gives O(log N + K). Handle edge cases like empty prefix, no matches, and duplicate functions.

Key Points to Mention

  • Choice of data structure: trie vs. sorted list vs. hash map with prefix keys
  • Time complexity of register() and findMatches() for each approach
  • Handling of duplicate argument type sequences and multiple functions with same signature
  • Edge cases: empty prefix, prefix longer than any sequence, no matches
  • Scalability considerations for large numbers of functions and frequent queries
  • Potential for concurrency if registration and matching happen simultaneously

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