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Uber·Software Engineer·Technical Phone Screen·Intermediate

Intermediate
May 2026

Summary

Uber SWE interview with a pipeline throughput optimization problem. The core trick is binary searching on the answer rather than trying to allocate budget greedily, which I didn't see immediately and cost me some time.

Questions Asked (1)

Q1

You have N services in a pipeline where total throughput equals the minimum throughput across all services. Each service can be scaled up at a cost, and scaling a service multiplies its throughput. Given a budget, how do you maximize the pipeline's overall throughput?

Algorithms & Data StructuresTechnical Trade-offs
Author's notes

Spent the first few minutes trying to think of a greedy approach, like always scaling the cheapest bottleneck first.

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AI HintsAI Generated

Suggested Approach

Model the problem as maximizing the minimum throughput after allocating budget to scale services, where scaling multiplies throughput. Use binary search on the target throughput to check feasibility: for each service, compute the minimum scaling factor needed to reach the target, then sum the costs and compare with the budget. Optimize by considering discrete scaling options or continuous cost functions.

Pro tip: Mention that in practice, scaling often has diminishing returns and discrete steps, so a greedy approach may not be optimal; binary search on the answer is a robust technique for bottleneck optimization problems.

1. Understand the problem and define variables

Clarify that total throughput is the minimum of all services' throughputs, and scaling a service multiplies its throughput by a factor. Define the budget and cost function for scaling each service.

2. Formulate as a decision problem

For a given target throughput T, determine if it's possible to scale services so that each service's throughput ≥ T, and the total cost ≤ budget. This involves computing the required scaling factor for each service and summing costs.

3. Choose an optimization strategy

Use binary search on T if the feasibility check is monotonic (higher T requires more budget). Alternatively, if scaling options are discrete, consider dynamic programming or greedy with priority queue, but binary search is often simpler.

4. Implement feasibility check efficiently

For each service, given current throughput and cost function, compute the minimal cost to achieve at least T. Sum these costs and compare with budget. Optimize by precomputing or using mathematical formulas.

5. Analyze complexity and edge cases

Discuss time complexity (e.g., O(N log(maxT)) for binary search) and handle cases where scaling is not possible (e.g., budget insufficient even for base throughput). Mention that if scaling factors are continuous, the problem may be solvable analytically.

Key Points to Mention

  • Bottleneck optimization: throughput is limited by the slowest service.
  • Binary search on the answer (target throughput) to find the maximum feasible T.
  • Feasibility check: for each service, compute required scaling and cost, sum costs, compare to budget.
  • Cost functions: linear, discrete steps, or diminishing returns affect the approach.
  • Trade-offs: scaling the bottleneck service may be most cost-effective, but multiple services might need scaling.
  • Complexity analysis: O(N log(maxT)) time, O(1) extra space for binary search.

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