NVIDIA·Software Engineer·Technical Phone Screen·Intermediate

IntermediatePrefer not to say

Apr 2026

Summary

NVIDIA software engineer coding round, just one question but it took up the whole session. The problem itself wasn't hard conceptually but getting the encoding scheme exactly right under pressure was annoying.

Questions Asked (1)

Design and implement an encode and decode function pair for a list of strings. The encoding format should store each string's length followed by the string itself and a delimiter character, and decoding must reconstruct the original list exactly.

Algorithms & Data StructuresAPI & IntegrationsTechnical Trade-offs

Author's notes

The scheme they wanted was length-prefix plus a separator, so something like '3foo#3lis#4jljl#' for ['foo','lis','jljl'].

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AI HintsAI Generated

Suggested Approach

Clarify the encoding format: for each string, write its length as a decimal number, then a delimiter (e.g., '#'), then the string itself. For decoding, parse the length, skip the delimiter, and extract exactly that many characters. Emphasize that the length prefix makes the encoding unambiguous even if strings contain the delimiter.

Pro tip: Mention that using a length prefix avoids delimiter collision issues, and discuss how this approach scales to large lists and arbitrary string content. Also, consider edge cases like empty strings and Unicode characters.

1. Clarify requirements and constraints

Ask about the expected input size, character set (ASCII vs Unicode), and whether the encoded string must be human-readable. Confirm that the delimiter is not part of the length representation.

2. Design the encoding format

For each string, output its length in decimal, followed by a delimiter (e.g., '#'), then the string. Concatenate all encoded strings. Example: ['ab', 'c'] -> '2#ab1#c'.

3. Implement the encode function

Iterate over the list, for each string compute its length, convert to string, and append length + delimiter + string to a result list. Finally, join the list into a single string.

4. Implement the decode function

Use an index pointer to traverse the encoded string. At each step, read characters until the delimiter to get the length, skip the delimiter, then extract that many characters as the next string. Repeat until the end.

5. Test and handle edge cases

Test with empty list, empty strings, strings containing the delimiter, and multi-digit lengths. Ensure the decoded list matches the original exactly.

Key Points to Mention

Length-prefix encoding avoids delimiter collision and is unambiguous.
Time complexity: O(n) for both encode and decode, where n is total characters.
Space complexity: O(n) for the encoded string and decoded list.
Handling of multi-digit lengths and delimiter parsing.
Edge cases: empty strings, empty list, strings with delimiter characters.
Potential trade-offs: using a fixed-width length vs variable-width, and readability vs efficiency.

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