← Google Interview Insights

Google·Software Engineer·Technical Phone Screen·Intermediate

Intermediate
Apr 2026

Summary

Google SWE interview with a file processing problem. Pretty straightforward premise but the scale angle is what makes it interesting.

Questions Asked (1)

Q1

You have a very large text file where each line contains a number. How do you find the maximum value in the file?

Algorithms & Data StructuresSystem DesignTechnical Trade-offs
Author's notes

My first instinct was to just read everything into memory and call it a day, which is obviously wrong when they say 'very large.' Had to backtrack and think about streaming line by line.

Create a free account to read the full note

AI HintsAI Generated

Suggested Approach

Start by clarifying the constraints: file size, memory limits, and whether the file fits in memory. Then propose a streaming solution that reads the file line by line, maintaining a running maximum, and discuss trade-offs like time complexity, I/O efficiency, and potential optimizations for very large files.

Pro tip: Mention that you would use memory-mapped I/O or parallel processing if the file is extremely large, but always emphasize correctness and simplicity first. Also, discuss how to handle edge cases like empty files or malformed lines.

1. Clarify requirements and constraints

Ask about file size, available memory, whether the file is static or streaming, and if the numbers are integers or floats. This shows you consider practical limitations before jumping to code.

2. Propose a streaming algorithm

Describe reading the file line by line, parsing each line as a number, and updating a running maximum. This uses O(1) memory and O(n) time, which is optimal for a single pass.

3. Discuss implementation details

Explain how to handle parsing errors, empty lines, and large numbers. Mention using buffered reading to reduce I/O overhead and possibly using a fast parsing library.

4. Consider optimizations for very large files

If the file is too large for a single machine or requires faster processing, discuss parallelizing by splitting the file into chunks, finding the max in each chunk, and then combining results. Also mention memory-mapped files or external sorting if needed.

5. Analyze trade-offs and edge cases

Compare the streaming approach with alternatives like loading into memory (if feasible) or using a database. Discuss time/space complexity, I/O bottlenecks, and how to handle edge cases like empty files or non-numeric lines.

Key Points to Mention

  • Streaming line-by-line processing to achieve O(1) memory usage
  • Time complexity O(n) where n is the number of lines
  • Handling edge cases: empty file, malformed lines, negative numbers
  • Using buffered I/O or memory-mapped files for efficiency
  • Parallel processing for extremely large files (e.g., MapReduce-style)
  • Trade-offs between simplicity, memory usage, and speed

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