Amazon·Software Engineer·Onsite - Coding / Algorithms·Intermediate

IntermediatePrefer not to say

May 2026

Summary

Amazon SWE coding round, got a Morse code decoding problem that looked deceptively manageable until the 'no character separator' part hit. The whole thing was about enumerating all valid partitions per word segment and combining them across words.

Questions Asked (1)

Given a Morse code string split into word segments by a known separator, decode all possible sentences. Within each word segment there are no character separators, so you need to find every valid way to partition each segment into valid Morse tokens, then combine across words to return all unique decoded sentences.

Algorithms & Data StructuresTechnical Trade-offs

Author's notes

My first instinct was a simple recursive split and I got the basic case working fast.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the problem constraints (e.g., Morse code mapping, separator, uniqueness of sentences) and then outline a solution that uses backtracking to generate all valid decodings for each word segment, followed by a Cartesian product to combine them. Discuss trade-offs between recursion/backtracking and dynamic programming, and mention how to handle duplicates and optimize for performance.

Pro tip: Emphasize the importance of pruning invalid paths early in the backtracking and using memoization to cache results for repeated subproblems, which shows you think about efficiency and scalability—key at Amazon.

1. Clarify requirements and constraints

Ask about the Morse code mapping (e.g., standard ITU), the word separator, whether the input is guaranteed to be valid, and if sentences should be unique. Confirm output format and edge cases.

2. Design decoding for a single word segment

Use backtracking to explore all possible partitions of the segment into valid Morse tokens. At each step, try taking 1 to 4 characters (since Morse codes are 1-4 symbols) and recurse if it's a valid code.

3. Combine decoded words across segments

After decoding each word segment into a list of possible words, compute the Cartesian product of these lists to form all possible sentences. Ensure uniqueness by using a set or by deduplicating at the end.

4. Optimize and handle duplicates

Apply memoization to cache results for each segment to avoid redundant computations. Discuss how to handle duplicate sentences that may arise from different partitions leading to the same word.

5. Analyze complexity and trade-offs

Explain time and space complexity, and discuss trade-offs between backtracking and dynamic programming. Mention potential optimizations like pruning invalid prefixes early.

Key Points to Mention

Backtracking with pruning for generating all valid partitions of a Morse segment.
Memoization to cache results for repeated subproblems and improve efficiency.
Cartesian product to combine word lists across segments, ensuring uniqueness.
Handling of edge cases: empty segments, invalid Morse codes, and duplicate sentences.
Time and space complexity analysis, including worst-case exponential scenarios.
Trade-offs between recursive backtracking and iterative DP approaches.

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