Hackerrank

Role: Backend Engineer II

College: Not Specified (Candidate had 2 years 9 months of experience)

Interview Date: Recently appeared (published Jan 2025)

Interview Type: Full-Time

Result: Rejected

Difficulty: OA: Medium to Hard. Code-Pair: Medium to Hard. System Design: Medium to Hard.

Rounds: 3 rounds (Online Coding Assessment, Code-Pair/DSA, High-Level System Design)

Topics Asked: Data Structures, Algorithms, System Design, Database Schema

Experience:

This candidate, with nearly 3 years of experience, shared their interview experience for a Backend Engineer II position at HackerRank after applying through the career site.

Online Coding Assessment (HackerRank Platform)

The assessment lasted 1 hour and featured an AI assistant. Three questions were asked one after the other. If all test cases passed for a solution, the AI provided a follow-up question; if some failed, hints were given.

• Question 1: LeetCode problem "Contiguous Array". The candidate was able to solve it.
• Follow-up 1 (Question 2): "If you are allowed to flip at most 1 value in the array i.e 0 to 1 or 1 to 0, calculate the longest subarray". The candidate was able to solve this as well.
• Follow-up 2 (Question 3): "Longest subarray with all prefixes of that subarray should have ones more than or equal to zeroes". The candidate couldn't pass all test cases for this.

After this round, the candidate received a call to schedule the interviews.

Code-Pair (DSA) Round (HackerRank Platform)

This round was 1 hour long and involved two questions.

• Question 1: Given log entries of the form "sender\_id receiver\_id transaction\_amount" (strings with digits), and an integer "threshold", return all suspicious user\_ids (those appearing in at least "threshold" transactions) sorted in ascending numerical order. The candidate solved this using a map.
• Question 2: A hard question on binary strings, which the candidate was also able to solve (exact question not remembered).

After this, the candidate received a call to schedule the system design interview.

High-Level System Design Interview (HackerRank Platform)

This interview lasted 1 hour, using an interface similar to draw.io.

• Question: Design a system similar to HackerRank, where companies can create online coding tests and users can attend them.

The candidate started with functional and non-functional requirements, then provided an overall high-level system design. They were asked to design the database schema and explained the question submission flow (when a user writes code and clicks "Run tests"). They discussed drawbacks of their approach and alternate ways.

The candidate did not receive the offer, attributing it to a lack of speed, and advised future candidates to practice extensively on the HackerRank platform.