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Amazon·Software Engineer·Technical Phone Screen·Intermediate

Intermediate
Jun 2026

Summary

Amazon SWE interview with a log-processing coding question. Pretty straightforward problem on the surface but they wanted the full complexity analysis too, which is where things got a bit more involved.

Questions Asked (1)

Q1

Given a list of log entries where each entry is a string containing a username and a timestamp, write an algorithm to find the username that appears most frequently. If there's a tie, returning any one of the tied users is acceptable. Walk through the time and space complexity of your approach.

Algorithms & Data Structures
Author's notes

Used a hash map to count occurrences then did a single pass to find the max.

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AI HintsAI Generated

Suggested Approach

Clarify the input format and assumptions, then propose a hash map solution that counts occurrences of each username in a single pass. After counting, iterate through the map to find the username with the maximum count, handling ties arbitrarily. Finally, analyze the time and space complexity.

Pro tip: Mention that you would use a hash map for O(1) average-case lookups, and discuss potential edge cases like empty input or malformed entries to show thoroughness.

1. Clarify the problem

Ask clarifying questions about the input format, such as how the username and timestamp are separated, whether timestamps are unique, and if the list can be empty or contain malformed entries.

2. Choose the right data structure

Select a hash map (dictionary) to store usernames as keys and their frequencies as values, enabling efficient counting.

3. Design the algorithm

Iterate through each log entry, extract the username, and update its count in the hash map. Then, traverse the map to find the username with the highest count.

4. Analyze complexity

State that the time complexity is O(n) for n log entries, and space complexity is O(u) where u is the number of unique usernames.

5. Discuss edge cases and optimizations

Mention handling empty input, ties, and potential memory optimizations if the number of unique usernames is very large.

Key Points to Mention

  • Hash map for O(1) average-case insertion and lookup
  • Single pass to count frequencies, second pass to find max
  • Time complexity: O(n) where n is number of log entries
  • Space complexity: O(u) where u is number of unique usernames
  • Handling ties by returning any tied user
  • Edge cases: empty list, malformed entries, large input

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