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

Intermediate

May 2026

Summary

Amazon SWE online assessment, one coding problem about simulating a parcel sorting process. Pretty straightforward simulation but the phrasing threw me off at first.

Questions Asked (1)

Given a permutation array representing a sorting sequence, find the minimum number of full passes required to process all elements in order (where each pass goes left to right and arranges any element that matches the next expected value).

Algorithms & Data Structures

Author's notes

The problem description is wrapped in this warehouse/parcel story which honestly made it harder to parse than the actual logic.

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AI HintsAI Generated

Suggested Approach

Clarify the problem statement and constraints first, then propose an efficient algorithm that tracks the positions of elements to determine the minimum number of passes. Explain that the number of passes equals the number of 'breaks' in the sequence where a smaller element appears after a larger one, plus one, and validate with examples.

Pro tip: Demonstrate awareness of edge cases like already sorted or reverse sorted arrays, and discuss how the solution scales for large inputs, showing you think about performance and robustness.

1. Understand the problem

Restate the problem in your own words and confirm details: what constitutes a pass, how elements are arranged, and what 'in order' means. Ask clarifying questions if needed.

2. Identify the key insight

Recognize that the minimum number of passes is determined by the number of times the sequence decreases when scanning left to right, as each decrease requires an additional pass.

3. Design the algorithm

Propose an O(n) solution: iterate through the permutation, count the number of indices i where arr[i] > arr[i+1], and return that count plus one.

4. Validate with examples

Walk through small examples (e.g., [1,2,3], [3,2,1], [2,1,3]) to verify the formula and ensure the logic holds for edge cases.

5. Analyze complexity and edge cases

State time and space complexity (O(n) time, O(1) space) and discuss edge cases like already sorted (1 pass) and reverse sorted (n passes).

Key Points to Mention

Definition of a pass and how elements are rearranged during each pass.
The relationship between the number of passes and the number of 'descents' in the permutation.
Time and space complexity of the proposed solution.
Edge cases: already sorted array, reverse sorted array, and arrays with duplicates (though permutation implies distinct).
Alternative approaches (e.g., simulation) and why they are less efficient.
Potential follow-up: how to handle streaming data or multiple queries.

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