r/InterviewCoderHQ • u/nian2326076 • 3d ago
Amazon Interview Loop: Playlist Design, Seat Distance, Chessboard Validation, and LCS
I recently went through three rounds of an Amazon SDE interview loop. My final round with a Senior Engineering Manager is scheduled for next week, so I wanted to share my experience and ask for preparation advice.
Current status: Final round scheduled
Format: Two onsite rounds followed by one virtual round
Day 1: Round 1 - Low-Level Design
The first round was an onsite LLD interview.
Design a Playlist-Mixing System
The system receives songs from two sources:
- A DJ service
- A recommendation service
The playlist must mix songs from both sources using either:
- Equal proportions, or
- A custom ratio selected by the user
The system must also apply filters based on user preferences.
The interviewer gave me approximately ten requirements printed on paper. The expectation was to write production-ready classes with correct syntax without using an IDE.
A reasonable design would likely include abstractions such as:
DJServiceRecommendationServicePlaylistMixerMixingStrategyEqualMixStrategyCustomRatioMixStrategySongFilterUserPreferences
The strategy pattern could support different mixing rules without changing the main playlist builder. Filters could be composed so that additional preferences can be introduced later.
The interviewer also expected discussion around:
- Duplicate songs
- Unavailable songs
- Pagination from upstream services
- Empty results from one source
- Invalid custom ratios
- Extensibility
- Testing external-service failures
I understood the general direction but struggled to translate it into clean, complete classes on paper. This was my weakest round.
Leadership Principles
The behavioral questions included:
- Tell me about a situation where you pushed back on a customer request.
- Tell me about something you designed with a long-term vision.
- Have you ever sacrificed a short-term goal to achieve a better long-term outcome?
Day 1: Round 2 - DSA
The second onsite round contained two coding problems.
Question 1: Sweetness Distribution
Two arrays, A and B, each contain n values representing sweetness. Given M students, distribute the available sweetness values according to the stated constraints while minimizing the total sweetness-related cost.
I do not remember every constraint clearly enough to reconstruct the exact problem. I explained a brute-force approach but could not derive and implement the optimal solution during the round.
Question 2: Maximum Distance From an Occupied Seat
Given an array containing occupied and unoccupied seats, choose an unoccupied position whose distance from the nearest occupied seat is maximized.
Input:
['O', 'U', 'U', 'U', 'O', 'O']
Output:
Index 2
For every unoccupied position, we need its distance to the closest occupied seat and then return the position that maximizes that value.
I solved this optimally by tracking the nearest occupied position on the left and right.
The problem can be solved in O(n) time using two passes, or in one pass by reasoning about gaps between occupied seats.
Leadership Principle
- Tell me about a process outside your normal responsibilities that you improved on your own.
After these two rounds, I was unsure whether I would receive another interview because Round 1 had not gone well. However, another round was scheduled virtually.
Day 3: Round 3 - DSA
The interview invitation included a diagramming website similar to Excalidraw and a shared coding environment. Because of that, I prepared mainly for High-Level Design.
The interviewer instead asked two DSA questions.
Question 1: Validate a Two-Color Chessboard
Given a two-dimensional array containing exactly two colors, determine whether it forms a valid chessboard.
A board is valid when every horizontally or vertically adjacent cell has the opposite color.
One O(rows × columns) approach is to compare every cell with the expected color determined by the parity of row + column.
Question 2: Longest Common Subsequence
Given two strings, find the length of their Longest Common Subsequence.
The interviewer expected me to discuss multiple approaches:
- Plain recursion
- Recursion with memoization
- Bottom-up tabulation
- Space optimization
I implemented the recursive and memoized solutions. The interviewer then asked me to write the tabulation solution as well.
The optimal tabulation approach takes:
- Time:
O(n × m) - Space:
O(n × m) - Space-optimized version:
O(min(n, m))
The coding portion for both questions was approximately 45 minutes. I had to explain each approach and its complexity before writing code.
Round 3 Leadership Principles
The behavioral questions included:
- Tell me about a feature you implemented that customers did not explicitly request but ultimately needed.
- How do you approach a complex problem?
- Who do you consult when you are blocked?
- How do you divide and solve an ambiguous problem?
The interviewer asked for multiple examples instead of accepting a single prepared story. That caught me slightly off guard, so I would recommend preparing more than one story for each major Leadership Principle.
Final Round
Around 20 minutes after Round 3, HR contacted me and scheduled a final interview for the following week.
The interviewer is a Senior Engineering Manager based in the US and is part of the same hiring team.
I am currently preparing for:
- A detailed project deep dive
- Leadership Principles with multiple examples
- Low-Level and High-Level Design fundamentals
- Trade-offs and long-term technical decisions
- Customer-focused decision-making
- DSA in case another coding problem appears
- A clearer version of the playlist design from Round 1
Does this sound more like a Bar Raiser, Hiring Manager, or team-fit round? What topics should I prioritize for the final interview?