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Uber·Software Engineer·Technical Phone Screen·Senior

SeniorPrefer not to say
May 2026

Summary

Uber coding screen with a pretty gnarly optimization problem involving pipeline throughput and budget constraints. Not a typical LeetCode grind question, felt more like a resource allocation puzzle with a twist.

Questions Asked (1)

Q1

You have a chain of services where each feeds into the next. Each service can be scaled up multiple times, and each scale-up has a throughput gain and a cost. Given a total budget, how do you choose which scale-ups to apply so that the end-to-end pipeline throughput (bottlenecked by the weakest service) is maximized?

Algorithms & Data StructuresTechnical Trade-offs
Author's notes

The bottleneck part is what trips you up first.

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AI HintsAI Generated

Suggested Approach

Model the problem as maximizing the minimum throughput across services under a budget constraint, where each service's throughput is a function of its scale-ups. Use binary search on the target throughput to check feasibility, then allocate budget to the bottleneck service until it's no longer the bottleneck, repeating until budget is exhausted.

Pro tip: Emphasize that the optimal solution often involves balancing services to similar throughput levels rather than over-scaling one service, and mention that greedy allocation works when scale-up gains are diminishing.

1. Define throughput functions and budget

For each service, create a function that maps the number of scale-ups to its throughput, considering the gain and cost of each scale-up. The overall pipeline throughput is the minimum of these functions.

2. Binary search on target throughput

Binary search over possible throughput values. For a given target T, compute the minimum cost to make each service achieve at least T throughput, then sum these costs and check if it's within budget.

3. Feasibility check via greedy allocation

For each service, determine the cheapest set of scale-ups that reaches T. Since scale-ups have varying gains and costs, use a greedy approach (e.g., sort by gain per cost) or dynamic programming if scale-ups are discrete and small in number.

4. Find optimal throughput and allocation

The binary search yields the maximum feasible T. Then, for that T, output the specific scale-ups chosen for each service to achieve T within budget.

5. Discuss complexity and trade-offs

Analyze time complexity (e.g., O(N log(maxT) * K) where K is scale-ups per service) and mention that if scale-ups are continuous, a greedy water-filling approach may be more efficient.

Key Points to Mention

  • Bottleneck principle: end-to-end throughput is limited by the slowest service.
  • Binary search on the answer to convert optimization to feasibility.
  • Greedy allocation for each service to meet a target throughput at minimum cost.
  • Diminishing returns: scale-ups may have decreasing throughput gains, affecting allocation.
  • Budget constraint: total cost of selected scale-ups must not exceed budget.
  • Trade-off between throughput and cost; sometimes not all budget needs to be spent.

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