My interview experience for SDE1 role

My Interview Experience at Z for the Role of SDE1: A Technical Journey

Recently, I interviewed at Z for the position of Software Development Engineer 1 (SDE1). The process was tough but offered a great learning experience. I want to share the rounds I went through, the technical questions I faced, and some insights from a friend who successfully cleared the interview.

The Interview Process

The interview process was composed of several rounds, each testing different skills like coding, problem-solving, and system design. Here’s a breakdown of what I faced:

Round 1: Online Coding Test

The first round was an online coding test, where I was given three algorithmic problems to solve within 90 minutes:

1. Longest Palindromic Substring

    I had to find the longest substring that reads the same backward.
    Approach: I used dynamic programming to solve this with a time complexity of O(n²).

2. Merge K Sorted Arrays

    The task was to merge K sorted arrays into one sorted array.
    Approach: Using a min-heap, I solved it with a time complexity of O(n log k), where n is the total number of elements.

3. Find the First Missing Positive Integer

    I was required to find the smallest missing positive integer in an unsorted array.
    Approach: I rearranged the array in place to achieve an O(n) time complexity.

I was able to solve all three problems and advanced to the next round.

Round 2: Advanced Online Coding Test

This round was more difficult than the first, featuring advanced algorithmic problems. I was given two hours to complete the following:

1. Find All Bridges in a Graph

    I needed to find all bridges in an undirected graph (edges that, if removed, would increase the number of components).
    Approach: I used Tarjan’s Algorithm, which has a time complexity of O(V + E).

2. Shortest Path in a Weighted Directed Acyclic Graph (DAG)

    I was tasked with finding the shortest path in a DAG with weighted edges.
    Approach: I used topological sorting followed by dynamic programming.

3. N-Queens Problem
    The classic N-Queens problem asked me to place N queens on an N×N chessboard so that no two queens attacked each other.
    Approach: I implemented backtracking and optimized it to handle larger N values.

I completed two out of three problems but struggled with the last one, which impacted my confidence going forward.

Round 3: Technical Interview I (Data Structures & Algorithms)

In this round, I had to solve coding problems in front of the interviewer, who focused on data structures and algorithms. Here are two problems I was asked:

1. Implement a Queue using Stacks

    The challenge was to implement a queue using two stacks. I walked through my approach, explaining how I achieved enqueue and dequeue operations and discussed their time complexities.

2. Diameter of a Binary Tree
    The interviewer asked me to calculate the longest path (diameter) of a binary tree. I used DFS (depth-first search) to find the diameter and handled edge cases like skewed trees.

The interviewer seemed satisfied with my approach, and I performed well in this round.

Round 4: Technical Interview II (System Design)

The fourth round focused on system design. I was asked to design a URL shortening service similar to Bit.ly. The interviewer wanted to know how I would:

• Store and retrieve the original and shortened URLs in a database.
• Handle the system’s scalability as user numbers grew.
• Deal with hash collisions when generating short URLs.

I made some errors in my approach, especially when it came to scalability. Although I covered the basics, I missed out on key points that led to some gaps in my design. I realized later that I needed to dive deeper into large-scale systems, and I didn’t perform as well as I had hoped.

Round 5: Advanced Technical Interview II (My Friend's Experience)

Unfortunately, I didn’t make it through the final technical round. However, my friend, who interviewed for the same position and was successfully placed at Z, shared his experience with me. Here’s what he faced:

Friend’s Experience:

Problem 1: Design a Scalable Notification System

• He was tasked with designing a system that could send millions of notifications to users in real-time.
• His explanation: He used message queues to manage large volumes of notifications and ensure delivery in batches. He also discussed load balancing and how to respect user preferences in real time.

Problem 2: Optimize a Rate-Limiting Algorithm

• The interviewer asked him to design and optimize a rate-limiting algorithm to control the number of requests a user can make to a service.
• His solution: He proposed a token bucket algorithm, which is efficient in handling bursts of traffic. He discussed how the algorithm could be implemented in a distributed system, using Redis for storage.

• Problem 3: Implement Consistent Hashing
• He was asked to implement consistent hashing to distribute load evenly across servers.
• His explanation: Consistent hashing is helpful when scaling distributed systems, as it minimizes the need to reassign keys when servers are added or removed. He walked through its implementation and how it could improve scalability.

Friend’s Reflection: According to him, the interviewer was keen on hearing trade-offs in his design. He stressed the importance of explaining why certain design decisions were made and how they could handle real-world scaling issues.

Round 6: Behavioral Interview

The final round was a behavioral interview, similar for both of us. I was asked questions such as:

• Describe a time when you had to meet a tight deadline. How did you handle it?

I shared an example from a past project where time management was critical. My friend, however, focused more on leadership and teamwork, which may have given him an advantage during this round.

What I Learned

Even though I didn’t make it through, the interview experience at Z taught me a lot. Here’s what I learned:

• Be ready for advanced topics: The advanced coding and system design rounds were far more difficult than I expected. It’s important to brush up on algorithms and distributed systems concepts.
• Practice system design: My friend’s success in the system design rounds shows how crucial it is to understand scalability, databases, and distributed systems in detail.
• Explain your thought process: Whether it’s a coding problem or system design, explaining your reasoning clearly is key to doing well.

Conclusion

Interviewing at Z was a challenging but valuable experience. Although I didn’t clear all the rounds, I learned a lot about what companies like Z expect from SDE1 candidates. If you're preparing for an SDE1 interview, focus on improving your coding skills, understanding system design, and preparing for behavioral questions.