Google·Software Engineer·Technical Phone Screen·Intermediate

IntermediatePrefer not to say

Apr 2026

Summary

Google SWE coding round with a string manipulation problem that looked deceptively straightforward. The checksum-based encoding angle threw me off a bit.

Questions Asked (1)

Given a string, a validation string, and a chunk length k, split the input string into substrings of length k. For each chunk, compute a checksum by summing the character values, then use that checksum (mod the length of the validation string) as an index into the validation string to pick a character. Return the string formed by concatenating all the picked characters in order.

Algorithms & Data StructuresTechnical Trade-offs

Author's notes

I started coding before I fully thought through the modulo indexing part and had to backtrack, which felt bad.

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AI HintsAI Generated

Suggested Approach

Start by clarifying edge cases and assumptions, then walk through a simple example to demonstrate understanding. Outline a step-by-step algorithm, analyze time and space complexity, and discuss potential optimizations or trade-offs.

Pro tip: Mention that you would handle the last chunk even if it's shorter than k, and discuss whether to use absolute or relative character values (e.g., ASCII) and how that affects the checksum.

1. Clarify Requirements and Edge Cases

Ask about input constraints, character encoding, handling of incomplete chunks, and validation string length. Confirm expected output for empty strings or k <= 0.

2. Walk Through an Example

Choose a small example and manually compute the output to verify understanding and uncover any ambiguities.

3. Design the Algorithm

Iterate over the input string in steps of k, compute the sum of character values for each chunk, take modulo length of validation string, and append the corresponding character.

4. Analyze Complexity and Trade-offs

State time complexity O(n) and space complexity O(n/k) for the output. Discuss alternative approaches like precomputing checksums or using a different indexing scheme.

5. Test and Validate

Propose test cases including normal cases, edge cases (empty string, k=1, k > length), and cases where checksum modulo validation length is zero.

Key Points to Mention

Character encoding (ASCII vs Unicode) and how it affects checksum calculation
Handling of the last chunk when its length is less than k
Modulo operation to ensure index is within bounds of validation string
Time and space complexity analysis
Potential optimizations for large inputs (e.g., streaming, parallel processing)
Edge cases: empty input, k <= 0, validation string empty

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