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Amazon·Software Engineer·Online Assessment (OA)·Junior

JuniorRejected
Aug 2024Remote

Summary

Took the Amazon SDE OA in August, three rounds covering DSA, an AI-assisted Spring Boot debugging section, and work simulation plus behavioral questions. Felt decent about all of it and then got rejected anyway, which stings when you can't even pinpoint what went wrong.

Questions Asked (2)

Q1

Given an array of integers, find the minimum total number of element replacements needed to make all values identical, where each operation replaces every occurrence of one value with another.

Algorithms & Data Structures
Author's notes

Pretty clean problem once you see it.

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AI HintsAI Generated

Suggested Approach

First, clarify the problem: each operation replaces all occurrences of one value with another, so the goal is to minimize the number of such operations to make all elements identical. The optimal strategy is to choose the most frequent element as the target, then replace all other distinct values one by one; the answer is the number of distinct values minus one. Alternatively, if the target is not the most frequent, the answer is the number of distinct values (replace all others to the target, then replace the target to the most frequent).

Pro tip: Demonstrate algorithmic maturity by discussing the time complexity (O(n) with a hash map) and edge cases (empty array, single element, all elements same). Also, mention that this is a greedy choice and briefly justify why it's optimal.

1. Clarify the problem

Restate the problem in your own words and ask clarifying questions about constraints, input size, and whether the array can be empty.

2. Identify the goal

Recognize that the goal is to minimize the number of replacement operations, where each operation replaces all occurrences of one value with another.

3. Determine the optimal target

The optimal target is the most frequent element because it minimizes the number of distinct values that need to be replaced.

4. Compute the answer

Count the number of distinct values. If the most frequent element is chosen as target, the answer is distinct_count - 1; otherwise, it's distinct_count.

5. Analyze complexity and edge cases

Discuss time and space complexity (O(n) time, O(n) space) and handle edge cases like empty array or single element.

Key Points to Mention

  • Use a hash map to count frequencies of each element.
  • The number of distinct values is key to the solution.
  • Greedy choice: pick the most frequent element as the final value.
  • Time complexity: O(n) with a single pass for counting.
  • Space complexity: O(n) for the hash map.
  • Edge cases: empty array (0 operations), single element (0 operations), all elements same (0 operations).

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

Q2

You are given a broken Spring Boot project. Identify the bugs and fix the code so that all provided test cases pass.

Technical Trade-offsAPI & Integrations
Author's notes

This one's interesting because the AI assistant is part of the setup, not just a convenience.

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AI HintsAI Generated

Suggested Approach

Start by running the tests to see failures, then systematically debug from configuration and dependencies up to business logic, fixing one issue at a time and re-running tests. Prioritize fixes that unblock the most tests and explain your reasoning as you go, highlighting trade-offs between quick fixes and robust solutions.

Pro tip: Before diving into code, check if the project builds and if dependencies are correctly resolved; many 'bugs' are actually misconfigurations or version conflicts. Also, use the test failure messages as your primary guide—they often point directly to the root cause.

1. Run Tests and Analyze Failures

Execute the test suite to identify which tests fail and examine error messages, stack traces, and assertion failures to pinpoint the areas of code causing issues.

2. Check Configuration and Dependencies

Verify application properties, bean definitions, and dependency versions (e.g., Spring Boot starter versions) to ensure the project is set up correctly and compatible.

3. Inspect and Fix Code Logic

Review the failing code paths, looking for common bugs like null pointer exceptions, incorrect annotations, missing @Autowired, or flawed business logic, and apply targeted fixes.

4. Re-run Tests and Iterate

After each fix, re-run the tests to confirm progress and catch any regressions, continuing until all tests pass.

5. Explain Trade-offs and Best Practices

Discuss why you chose certain fixes over others, considering maintainability, performance, and alignment with Spring Boot conventions, and mention any potential improvements.

Key Points to Mention

  • Systematic debugging approach: start from high-level configuration and work down to detailed logic.
  • Importance of reading test failure messages and stack traces carefully.
  • Common Spring Boot pitfalls: incorrect annotations, missing dependencies, misconfigured properties.
  • Trade-offs between quick fixes and long-term maintainable solutions.
  • Use of Spring Boot testing features like @SpringBootTest and @MockBean.
  • Verification through iterative test runs and ensuring no regressions.

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