Google·Software Engineer·Technical Phone Screen·Intermediate

Intermediate

Apr 2026

Summary

Google SWE interview with a string manipulation problem dressed up as anti-spam logic. One question, fairly mechanical, the advice was basically to blow through it fast so you have time left over.

Questions Asked (1)

Given an email string, a verification string, and a constant k, slice the email into chunks of k characters, map each character to a number (letters a-z map to 1-25, and certain punctuation characters map to 26-28), sum each chunk, then use that sum mod the length of the verification string to pick a character from it. Concatenate all those characters and return the result.

Algorithms & Data Structures

Author's notes

The problem was framed as some kind of spam detection system which made it sound fancier than it was.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the mapping rules and edge cases, then walk through a small example to validate your understanding. Outline a step-by-step algorithm that handles chunking, character mapping, summation, modulo indexing, and concatenation, and analyze its time and space complexity.

Pro tip: Mention that you would precompute the character-to-number mapping in a dictionary for O(1) lookups, and discuss how to handle edge cases like empty strings or k larger than the email length.

1. Clarify the problem

Ask questions to confirm the mapping of letters and punctuation, the behavior when the email length is not a multiple of k, and what to do if the verification string is empty.

2. Design the algorithm

Break the problem into steps: slice the email into chunks of size k, map each character to its numeric value, sum each chunk, compute sum modulo the length of the verification string, and pick the corresponding character.

3. Walk through an example

Choose a small email, verification string, and k, and manually compute the output to verify the algorithm and catch any misunderstandings.

4. Analyze complexity

State that the time complexity is O(n) where n is the length of the email, and space complexity is O(n) for the output string (or O(1) if we build it incrementally).

5. Discuss edge cases and optimizations

Cover cases like empty email, k=0, non-alphanumeric characters, and suggest using a precomputed mapping array for efficiency.

Key Points to Mention

Character mapping: a-z to 1-25, and specific punctuation to 26-28 (e.g., space=26, '.'=27, ','=28).
Chunking the email into substrings of length k, handling the last chunk if it's shorter.
Summing the mapped values of each chunk and taking modulo the length of the verification string.
Using the modulo result as an index to select a character from the verification string.
Concatenating the selected characters to form the final result.
Time and space complexity analysis, and potential optimizations like precomputing the mapping.

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