Enforce ordered execution across threads

Quick Overview

Enforce ordered execution across threads evaluates algorithm design, data structures, correctness, complexity, edge cases, and implementation details in a realistic interview setting. A strong answer states assumptions, handles edge cases, explains trade-offs, and shows how to validate the result clearly.

Enforce ordered execution across threads

Company: Uber

Role: Software Engineer

Category: Coding & Algorithms

Difficulty: medium

Interview Round: Onsite

Implement a class with three methods alpha(), beta(), and gamma() that may be called by three different threads in arbitrary order, but must print their outputs in the fixed order A, B, C for N cycles. Use synchronization primitives to ensure ordering without busy-waiting, discuss fairness and potential deadlocks, and analyze the performance implications.

Quick Answer: Enforce ordered execution across threads evaluates algorithm design, data structures, correctness, complexity, edge cases, and implementation details in a realistic interview setting. A strong answer states assumptions, handles edge cases, explains trade-offs, and shows how to validate the result clearly.

Solution

# Solution Alignment The prompt asks for an implementation-level answer. The safest way to present it is to define the state, maintain clear invariants, then walk through complexity and tests. ## Problem Restatement Implement a class with three methods alpha(), beta(), and gamma() that may be called by three different threads in arbitrary order, but must print their outputs in the fixed order A, B, C for N cycles. Use synchronization primitives to ensure ordering without busy-waiting, discuss fairness and potential deadlocks, and analyze the performance implications. ## Recommended Approach Start with a brute-force baseline to confirm correctness, then identify the repeated work or ordering property that enables a better data structure such as a hash map, heap, stack, queue, two pointers, prefix sums, BFS/DFS, or dynamic programming. Write the implementation around a small invariant and test that invariant directly. ## Correctness The implementation should maintain an invariant after each loop or operation that directly matches the problem statement. At termination, that invariant implies the returned value has considered every valid candidate exactly once, or has preserved the required data-structure state after every API call. ## Complexity State the baseline complexity and the optimized complexity. For most interview constraints, justify why the optimized approach meets the expected input size. ## Edge Cases and Tests Empty and singleton inputs, duplicates, ties, invalid inputs, boundary values, and tests that exercise the main invariant.
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Aug 1, 2025, 12:00 AM
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Enforce ordered execution across threads

Implement a class with three methods alpha(), beta(), and gamma() that may be called by three different threads in arbitrary order, but must print their outputs in the fixed order A, B, C for N cycles. Use synchronization primitives to ensure ordering without busy-waiting, discuss fairness and potential deadlocks, and analyze the performance implications.

Clarifying Questions to Ask Guidance

  • Clarify input sizes, value ranges, mutability, return format, and tie-breaking.
  • State the target time and space complexity before coding.
  • Call out edge cases such as empty inputs, duplicates, invalid values, overflow, and boundary sizes.

What a Strong Answer Covers Guidance

  • A clear algorithm with the right data structures and enough pseudocode or code-level detail to implement it.
  • A correctness argument that explains why the algorithm covers all required cases.
  • Time and space complexity, plus at least one alternative approach when relevant.
  • Focused tests for normal cases, edge cases, and failure modes.

Follow-up Questions Guidance

  • How would the approach change if the input were streaming or too large for memory?
  • What invariants would you assert in production code?
  • Which tests would catch off-by-one, duplicate, or tie-breaking bugs?

Submit Your Answer to Earn 20XP

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