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SoFi·Software Engineer·Technical Phone Screen·Intermediate

Intermediate
Jul 2026

Summary

SoFi software engineering interview with a simulation-based coding problem. The question was more involved than I expected for a phone screen, definitely not a standard leetcode grind.

Questions Asked (1)

Q1

You have a class representing a collection of obstacle course runs. Implement a method that takes an in-progress run and returns the probability it will match or beat the current personal best, estimated via 10,000 Monte Carlo simulation trials. Each trial fills in the remaining obstacles by sampling from historical times recorded by other runs that reached each obstacle, including incomplete runs.

Algorithms & Data StructuresTechnical Trade-offs
Author's notes

The setup took me a while to internalize.

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AI HintsAI Generated

Suggested Approach

Start by clarifying the problem and assumptions, then outline a Monte Carlo simulation approach: for each trial, sample completion times for remaining obstacles from historical data, compute total time, and compare to personal best. Finally, discuss implementation details, edge cases, and trade-offs.

Pro tip: Mention that you would use the empirical distribution of historical times and handle missing data carefully, and that you would optimize by precomputing distributions or using vectorized operations for performance.

1. Clarify Requirements and Assumptions

Ask questions to understand the data structure, historical data availability, and definition of 'match or beat'. Confirm that incomplete runs provide valid samples for obstacles they reached.

2. Design the Simulation Algorithm

Outline the Monte Carlo loop: for each trial, for each remaining obstacle, randomly sample a time from the historical times for that obstacle, sum with the in-progress run's time so far, and compare to personal best.

3. Handle Data and Edge Cases

Discuss how to handle obstacles with no historical data (e.g., skip, use default, or fail gracefully), and ensure sampling is done correctly (e.g., with replacement).

4. Implement Efficiently

Suggest optimizations: pre-group historical times by obstacle, use arrays for fast sampling, and consider parallelization or vectorization for 10,000 trials.

5. Validate and Discuss Trade-offs

Mention testing with known distributions, and discuss trade-offs between accuracy and performance, and between different sampling strategies.

Key Points to Mention

  • Monte Carlo simulation: 10,000 trials to estimate probability.
  • Sampling from empirical distributions of historical times per obstacle.
  • Handling incomplete runs: they contribute data for obstacles they reached.
  • Edge cases: obstacles with no historical data, zero variance, etc.
  • Performance considerations: precomputation, vectorization, memory usage.
  • Statistical validity: independence assumption, sample size sufficiency.

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