PhonePe | Maching Coding | 90 Mins | 3-5 YOE | March 2025
Summary
This post details a 90-minute machine coding interview at PhonePe, where I was asked to design the backend for an interactive hackathon platform, including functionalities like problem management, user registration, scoring, filtering, and recommendations.
Full Experience
Duration: 90 Mins Coding + 15 Mins Evaluation
PhonePe is conducting its annual hackathon and wants to create an interactive platform to host the event. It will be a 2 day event and contestants need to maximize their score over this period by either solving more problems or more difficult problems. Design the backend to support this platform.
Mandatory Functionalities
The system should have the capability to add problems to the Questions Library. Contestants should be able to register themselves with their name and their department name. A problem should have attributes like description, tag, difficulty level (easy, medium, hard), score. Contestants should be able to filter problems based on difficulty level or tags and sort them based on score (design should be extensible to other attributes ) A contestant should be able to solve a problem as well as get the list of problems solved by him/her. A contestant should be able to see the number of users that have solved a given problem and average time taken to solve that problem. Scoring strategy for a problem could simply be to award the score assigned for the problem or could be something different like a combination of score and time. Return the current leader of the contest Users should be able to get curations like Top 10 most liked problems of a certain tag. Extension Problem
On solving a problem, users should get a recommendation of top 5 problems based on relevance The recommendation strategy for problems could simply be similar tags or extensible to include other factors like number of users who have solved a particular problem or a combination of factors ( Design should be extensible). Capabilities
Below are various functions that should be supported with necessary parameters passed. These are just suggestions, the signatures can be altered as long as the functionalities are provided.
Registering a problem - addProblem() Registering a user - addUser() Fetch the list of problems - fetchProblems() - Should take as input filtering and sorting criterias and return all matching problems in the right order. The result should contain problem attributes like name, tag, difficulty level, score etc. Should also display number of users who have solved a problem and the average time taken for that problem Solve a problem - solve() - Exposed to a contestant to mark a problem as solved [ For the extension problem, this function should return next 5 recommended problems ] Fetch solved problems for a user - fetchSolvedProblems() - Fetch the list of solved problems for a user Get leader - getLeader() - Returns the name and department of the leader Get top n liked problems of a certain tag - getTopNProblems() Guidelines
You should store the data in-memory using a language-specific data-structure. Implement clear separation between your data layers and service layers. Simple and basic function are expected as entry point - no marks for providing fancy * restful API or framework implementation Because this is a machine coding round, heavy focus would be given on data modeling, code quality etc, candidate should not focus too much time on algo which compromises with implementation time Expectations:
Your code should cover all the mandatory functionalities explained above. Your code should be executable and clean. Your code should be properly refactored, and exceptions should be gracefully handled. Appropriate errors should be displayed on the console How will you be evaluated?
Code Should be working Code readability and testability Separation Of Concerns Abstraction Object-Oriented concepts. Language proficiency. Scalability
Interview Questions (1)
Duration: 90 Mins Coding + 15 Mins Evaluation
PhonePe is conducting its annual hackathon and wants to create an interactive platform to host the event. It will be a 2 day event and contestants need to maximize their score over this period by either solving more problems or more difficult problems. Design the backend to support this platform.
Mandatory Functionalities
The system should have the capability to add problems to the Questions Library. Contestants should be able to register themselves with their name and their department name. A problem should have attributes like description, tag, difficulty level (easy, medium, hard), score. Contestants should be able to filter problems based on difficulty level or tags and sort them based on score (design should be extensible to other attributes ) A contestant should be able to solve a problem as well as get the list of problems solved by him/her. A contestant should be able to see the number of users that have solved a given problem and average time taken to solve that problem. Scoring strategy for a problem could simply be to award the score assigned for the problem or could be something different like a combination of score and time. Return the current leader of the contest Users should be able to get curations like Top 10 most liked problems of a certain tag. Extension Problem
On solving a problem, users should get a recommendation of top 5 problems based on relevance The recommendation strategy for problems could simply be similar tags or extensible to include other factors like number of users who have solved a particular problem or a combination of factors ( Design should be extensible). Capabilities
Below are various functions that should be supported with necessary parameters passed. These are just suggestions, the signatures can be altered as long as the functionalities are provided.
Registering a problem - addProblem() Registering a user - addUser() Fetch the list of problems - fetchProblems() - Should take as input filtering and sorting criterias and return all matching problems in the right order. The result should contain problem attributes like name, tag, difficulty level, score etc. Should also display number of users who have solved a problem and the average time taken for that problem Solve a problem - solve() - Exposed to a contestant to mark a problem as solved [ For the extension problem, this function should return next 5 recommended problems ] Fetch solved problems for a user - fetchSolvedProblems() - Fetch the list of solved problems for a user Get leader - getLeader() - Returns the name and department of the leader Get top n liked problems of a certain tag - getTopNProblems() Guidelines
You should store the data in-memory using a language-specific data-structure. Implement clear separation between your data layers and service layers. Simple and basic function are expected as entry point - no marks for providing fancy * restful API or framework implementation Because this is a machine coding round, heavy focus would be given on data modeling, code quality etc, candidate should not focus too much time on algo which compromises with implementation time Expectations:
Your code should cover all the mandatory functionalities explained above. Your code should be executable and clean. Your code should be properly refactored, and exceptions should be gracefully handled. Appropriate errors should be displayed on the console How will you be evaluated?
Code Should be working Code readability and testability Separation Of Concerns Abstraction Object-Oriented concepts. Language proficiency. Scalability