Amazon·Software Engineer·Technical Phone Screen·Intermediate

Intermediate

Jun 2026

Summary

Amazon SWE interview with a string decoding problem. Pretty straightforward coding round, nothing too wild, but the implementation details matter more than you'd expect.

Questions Asked (1)

Given a Morse code encoded string where single spaces separate letters and a different delimiter (like ' / ') separates words, write a function to decode it back to plain English.

Algorithms & Data StructuresTechnical Trade-offs

Author's notes

I built a hardcoded map of Morse patterns to letters, split on the word delimiter first, then split each chunk on single spaces.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the encoding rules and edge cases, then propose a hash map for Morse-to-letter lookup and a two-level split (space for letters, ' / ' for words). Discuss time/space complexity and potential optimizations like streaming or trie-based decoding.

Pro tip: Mention that you'd validate the input and handle invalid Morse sequences gracefully, and discuss how to extend the solution for real-time decoding or large inputs—showing you think beyond the basic algorithm.

1. Clarify requirements and edge cases

Ask about the exact delimiters, case sensitivity, handling of invalid codes, and whether the input can be empty or contain extra spaces.

2. Choose data structures

Use a hash map (dictionary) for O(1) Morse-to-letter lookup, and consider a trie if decoding needs to be prefix-based or streaming.

3. Design the algorithm

Split the input by ' / ' to get words, then split each word by ' ' to get Morse codes, map each code to a letter, and join letters into words.

4. Analyze complexity and trade-offs

Discuss O(n) time and space, and compare approaches like hash map vs. trie, or in-place decoding vs. building new strings.

5. Test and handle errors

Walk through examples, including edge cases like empty input, unknown codes, and multiple spaces; decide on error handling strategy.

Key Points to Mention

Use a hash map for O(1) Morse code lookup.
Split by ' / ' for words and ' ' for letters.
Time complexity O(n) where n is the length of the encoded string.
Space complexity O(n) for the output and O(1) for the lookup table.
Handle invalid Morse codes by either skipping, throwing an error, or using a placeholder.
Consider streaming or trie-based decoding for large or real-time inputs.

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