Amazon Interview Questions and Experience

1. Technical Questions

1. Explain the difference between Array and Linked List.
   An array has fixed size and allows random access in O(1). A linked list is dynamic and allows faster insertions/deletions but slower access.
2. What is the difference between Stack and Queue?
   A stack uses LIFO (Last In First Out) while a queue uses FIFO (First In First Out). Both are linear data structures with different access orders.
3. How do you detect a cycle in a linked list?
   Use Floyd’s Cycle Detection Algorithm (two pointers, slow and fast). If they meet, a cycle exists.
4. Write a program to reverse a string.
   Iterate from end to start or use two-pointer swapping. In Java: new StringBuilder(str).reverse().toString().
5. Explain HashMap in Java.
   HashMap stores key-value pairs using hashing. Average complexity is O(1) for put/get operations, though collisions may degrade performance.
6. How do you implement a queue using two stacks?
   Use one stack for enqueue, another for dequeue. When dequeueing, transfer elements if needed. This ensures FIFO behavior.
7. Explain Binary Search and its complexity.
   Binary Search repeatedly divides a sorted array to find an element. Time complexity is O(log n).
8. What is a Deadlock in operating systems?
   Deadlock occurs when processes wait indefinitely for resources locked by each other. Four conditions: mutual exclusion, hold & wait, no preemption, circular wait.
9. Difference between SQL INNER JOIN and LEFT JOIN.
   INNER JOIN returns matching records from both tables. LEFT JOIN returns all records from left table and matched records from right table.
10. What is the time complexity of QuickSort?
    Average case O(n log n). Worst case O(n²) when the pivot is poorly chosen.

Fresher

1. What should you focus on while preparing for an Amazon fresher interview?
   Focus on data structures, algorithms, OOP, and problem-solving. Practice coding questions on platforms like LeetCode and prepare behavioral answers.
2. What kind of projects should freshers highlight in interviews?
   Highlight academic or personal projects that show problem-solving, coding, or teamwork. Even small projects using real-world data or APIs add value.

Developer

1. What is the difference between Amazon S3 and EBS?
   S3 is an object storage service for unstructured data. EBS is block storage attached to EC2 instances for persistent volumes.
2. How would you design a scalable login system for millions of users?
   Use load balancers, session management, caching, and database sharding. Include failover and security measures like encryption.

Analyst

1. How do you handle missing data in a dataset?
   Methods include removal, mean/median imputation, or using predictive models. Choice depends on dataset size and importance of the variable.
2. What is A/B testing and why is it important?
   A/B testing compares two versions of a feature to measure impact on metrics. It helps in data-driven decision-making.

AWS

1. What is Auto Scaling in AWS?
   Auto Scaling automatically adjusts the number of EC2 instances to handle load efficiently, optimizing performance and cost.
2. What is the difference between IAM roles and IAM policies?
   IAM policies define permissions. IAM roles are identities with those permissions, assumed by users, applications, or services.

Manager

1. How do you manage a team under tight deadlines?
   Set priorities, delegate effectively, monitor progress, and keep communication open. Motivate the team while ensuring realistic goals.
2. How do you handle conflicts within your team?
   Address conflicts early by listening to both sides, finding common ground, and encouraging collaboration to maintain team harmony.

1. Tell me about a time when you worked in a team under pressure.
   I described a project with tight deadlines. I divided tasks, communicated progress regularly, and supported teammates, ensuring the project finished successfully.
2. How do you handle disagreements with a colleague?
   I listen to their perspective, share my reasoning, and look for a middle ground. If needed, I escalate respectfully to maintain progress.
3. Describe a situation where you took ownership of a project.
   In my previous role, I led a feature rollout. I managed requirements, coordinated with teams, and resolved issues, delivering on time with quality.
4. How do you ensure clear communication in cross-functional teams?
   I use simple, concise language, document requirements, and hold regular sync meetings. I also confirm understanding by summarizing key points.
5. Amazon values leadership principles. Which one resonates most with you and why?
   Customer Obsession resonates most with me. I always consider the end user’s needs and make decisions that improve customer experience.

Candidate Background: Final year B.Tech CSE student at Bennett University. Internship at ZS Associates. Strong focus on DSA and projects.

Interview Process They Faced

• Online Assessment: 2.5 hours. Code debugging, two coding questions, workstyle assessment, reasoning ability.
• Round 1 (Technical): Project discussion. Two coding problems.
• Round 2 (Technical): Leadership questions using STAR. One hard coding problem.
• Round 3 (Bar Raiser): Resume and behavioral discussion tied to Leadership Principles. Two coding problems.

Questions Asked

• OA: One easy and one hard coding. Debug tasks. Aptitude and workstyle.

Round 1:

• Find K Closest Elements in sorted array. Approach: binary search then two pointers.
• Rotting Oranges. Approach: BFS with queue.

Round 2:

• Word Search II variant. Required counting occurrences in grid. Discussed brute force and optimal.

Bar Raiser:

• Design a circular queue with fixed size. Implement functions and handle edge cases.
• Lowest Common Ancestor in a BST. Explain recursion flow and stack behavior.

Outcome & Difficulty Level: Selected as SDE-1. Difficulty: Moderate to Hard. Clear explanations, clean code, and dry runs were important.

Candidate Background: Software Engineer with industry experience. Tech stack across backend and systems. Applied through Amazon Careers under University Talent Acquisition.

Interview Process They Faced

• Online Assessment: One easy and one medium DSA problem. Work simulation modules. Behavioral MCQs.
• Round 1 (DSA): Single graph problem. Full coding with I/O handling.
• Round 2 (DSA): Maps and hashing based problem.
• Round 3 (System Design): Design a bookstore and count occurrences of a word in a given book. Discussed classes, methods, and data flow. Project deep dive.
• Round 4 (Mixed): Work deep dive for 40 minutes. Medium sliding window problem.

Questions Asked

OA: DSA coding. Work simulation on decision making and customer issues. Behavioral MCQs.

• Round 1: Currency converter graph problem. Choice of data structure and parsing.
• Round 2: Hash map based problem.
• Round 3:Bookstore design. Class design and search strategy. Project impact and approach.
• Round 4: Sliding window medium problem. Role and architecture discussion.

Outcome & Difficulty Level: Selected as SDE-1 after later HR confirmation. Difficulty: Moderate. Expect depth in DSA, clear design thinking, and detailed project discussions.