Software Engineer · Full Journey · Coding

Confluent — Software Engineer ❌ Failed

Level: Senior-Level

Round: Full Journey · Type: Coding · Difficulty: 7/10 · Duration: 180 min

Topics: Data Structures, System Design, Algorithms

Location: San Francisco Bay Area

Interview date: 2025-06-30

Got offer: False

Summary

Round 1: Phone Screen

Question: Implemented Windowed Map data structure with put and get operations.

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Round 2: Virtual Onsite (Coding)

Question: Implemented tail -n API to return the last n lines of a file.

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Round 3: Virtual Onsite (Coding)

Question: Modified word search problem to handle "AND/OR" conditions.

Details

Phone Screen: Windowed Map

I had to design a data structure called WindowedMap that stores values associated with keys and timestamps. The structure must support inserting values and retrieving values within a specific time window.

class WindowedMap { void put(String key, int value, long timestamp); List<Integer> get(String key, long startTime, long endTime); }

Operations:

• put(key, value, timestamp): Insert a value associated with the key at the given timestamp.
• get(key, startTime, endTime): Return all values associated with the key whose timestamps fall within the inclusive time range [startTime, endTime].

Example:

` put("a", 5, 10) put("a", 7, 12) put("a", 3, 20)

get("a", 10, 15) // Returns [5, 7] `

Constraints:

• Timestamps are non-negative integers.
• Values for each key may arrive out of order.
• Multiple values may share the same timestamp.

Follow-ups:

• Optimize for very large numbers of events per key.
• Assume timestamps for each key are strictly increasing.
• Support an operation: List<Integer> getLast(String key, long windowSize) to return values within the last windowSize time units from the most recent timestamp.

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Virtual Onsite Coding 1: tail -n API

I needed to implement an API that returns the last n lines of a file, similar to the Unix command tail.

List<String> tail(String filePath, int n);

Example:

` File contents: line1 line2 line3 line4 line5

tail(file, 2) // Returns ["line4", "line5"] `

Constraints:

• The file can be extremely large (e.g., 100GB).
• The solution must avoid loading the entire file into memory.

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Virtual Onsite Coding 2: Word Search

Initially, I thought it was a standard word search problem. The first part, searching for a single word, was standard. However, the second part was different from commonly asked interview questions. I had to handle search strings like: "Hello AND World OR is".