Allen Digital Interviews

You are part of a cab aggregator company, Allen Cabs, similar to Ola/Uber. As part of the Driver Billing team, you need to build a system that periodically generates bills for drivers based on the distance they've driven.

Platform Capabilities:

Drivers are onboarded to Allen Cabs and assigned a unique ID.

Vehicles are classified into three categories based on their model:

Economy

Premium

Luxury

Billing is based on the distance driven during trips, which can be:

Intra-city

Outstation

Billing Rates:

Intra-city:

Economy – ₹5/km

Premium – ₹12/km

Luxury – ₹15/km

Outstation: Charges are 2x of intra-city rates.

Cancellation Policy:

If a driver cancels the trip → fine of ₹10.

If a customer cancels the trip → driver is compensated ₹10.

Bonus Requirements (optional):

Variable cancellation fee based on trip type and vehicle category.

Ability to generate bills for a given time interval.

Drivers can either use:

Personal vehicles, or

Leased vehicles (leased from Allen Cabs, Allen charges x% of the bill as commission).

Method Signatures & Sample Inputs

AddDriver
AddDriver("Sachin", "+91-9936673000", "D101")
AddDriver("Ramesh", "+91-9936673011", "DL_02")
AddDriver("Manjunath", "+91-9936673010", "DL_03")

AddVehicle
AddVehicle("KA-01-2222", "Maruti Suzuki", "ECONOMY")

AddVehicle("KA-01-2223", "Ertiga", "PREMIUM")

MapDriverToVehicle
MapDriverToVehicle("Ramesh", "KA-01-2222")
MapDriverToVehicle("Manjunath", "KA-01-2223")

AddTrip
AddTrip(50, 1723116023, 1723117023, "INTRACITY", "COMPLETED", "Ramesh")
AddTrip(1050, 1723116023, 1723117023, "OUTSTATION", "COMPLETED", "Ramesh")
AddTrip(50, 1723116023, 1723117023, "INTRACITY", "CANCELED_CUSTOMER", "Ramesh")
AddTrip(50, 1723116023, 1723117023, "OUTSTATION", "CANCELED_DRIVER", "Manjunath")
AddTrip(70, 1723116023, 1723117023, "OUTSTATION", "COMPLETED", "Manjunath")

GetBill
GetBill("Ramesh") => (50 * 5) + (1050 * 10) + 10 = ₹10,560
GetBill("Manjunath") => -10 + (70 * 12 * 2) = ₹1,670

The interviewer was quite experienced. We began by discussing my previous projects and work experience. Then, I was asked to design a Ticket Booking System similar to IRCTC.

Here’s what I covered:

• Identified and discussed core entities and their relationships.
• Asked for and incorporated the interviewer’s feedback throughout the discussion.
• Transitioned into the High-Level Design, covering components and request flow.
• Toward the end, I was asked to add support for User Preferences (like berth choice).

I discussed possible design patterns that would allow such changes to be accommodated in a scalable and maintainable way.

Explain the linked list data structure and describe how to reverse a linked list.

Describe the heap data structure and its internal implementation.

Explain the Tree data structure. Additionally, two easy questions related to trees were discussed, specifically referencing problems like finding the diameter and height of a tree.

Solve the Alien Dictionary problem using graph algorithms.

Explain the React useContext hook, including its features, and write code demonstrating its usage.

Allen Digital is developing an online test proctoring system to monitor students during remote examinations. As part of the development team, you need to implement the core monitoring and alert system.

Expectations and Guidelines: ● Time Allotted: 90 minutes ● Internet Usage: You may use the internet only for syntax references. ● Programming Language: You may use any language of your choice. ● External Libraries: Do not use any external libraries. All code should be written by you. ● Make sure that you have working and demonstrable code for all requirements. ● Use of proper abstraction, separation of concerns is required. ● Code should easily accommodate new requirements with minimal changes. ● Proper exception handling is required. ● Code should be modular, readable and unit-testable.

Important Notes: ● Do not use any database store, use in-memory data structure. ● Do not create any UI for the application. ● Do not build a Command line interface. Executing test cases or a simple Main function should be sufficient. ● Do not make any assumptions; please ask if clarification is needed.

Evaluation Metrics: Your code will be evaluated based on: ● Functional Correctness ● Completeness ● Exception Handling ● Design Pattern Implementation

Platform Capabilities:

1. Students can register for online tests with their unique ID, name, and email.
2. Tests are defined with a unique ID, subject, duration, and start time.
3. The system monitors various activities during a test: ○ Tab switching (browser tab changed) ○ Focus loss (student not looking at the screen) ○ Multiple faces detected ○ No face detected ○ Suspicious object detected
4. Each activity type has a severity level: ○ LOW: Warning only (focus loss < 5 seconds) ○ MEDIUM: Potential cheating (multiple tab switches, focus loss > 5 seconds) ○ HIGH: Definite violation (multiple faces, suspicious objects)
5. The system should generate alerts based on these activities: ○ For LOW severity: Record the incident and continue ○ For MEDIUM severity: Issue a warning to the student ○ For HIGH severity: Flag the test for review and notify the proctor
6. After 3 MEDIUM severity incidents or 1 HIGH severity incident, the system should automatically pause the test and require proctor intervention. Bonus Capabilities:
7. Implement a time-weighted severity system where repeated violations in a short timeframe escalate severity.
8. Add a feature to record snapshots (text representation) at regular intervals for later review.
9. Implement an appeals system where students can provide explanations for flagged activities.
10. Add a statistical analysis feature to identify unusual patterns across multiple students taking the same test. Test Cases:

// Register Students 
RegisterStudent("ST001", "Vikram Singh", "vikram@example.com") RegisterStudent("ST002", "Anjali Desai", "anjali@example.com") 
// Create Tests 
CreateTest("TEST001", "JEE Advanced Physics", 180, 1723116023) CreateTest("TEST002", "NEET Biology", 120, 1723126023) 
// Register Students for Tests 
EnrollStudentInTest("ST001", "TEST001") 
EnrollStudentInTest("ST002", "TEST001") 
EnrollStudentInTest("ST002", "TEST002") 
// Start Tests 
StartTest("ST001", "TEST001", 1723116023) 
StartTest("ST002", "TEST001", 1723116023)
// Record Activities 
RecordActivity("ST001", "TEST001", "TAB_SWITCH", 1723116100) RecordActivity("ST001", "TEST001", "FOCUS_LOSS", 1723116200, 3) // 3 seconds 
RecordActivity("ST001", "TEST001", "FOCUS_LOSS", 1723116300, 10) // 10 seconds 
RecordActivity("ST002", "TEST001", "MULTIPLE_FACES", 1723116400) 
// Get Student Violations 
GetViolations("ST001", "TEST001") 
// Expected: 2 violations (1 LOW, 1 MEDIUM) 
// Check Test Status 
GetTestStatus("ST001", "TEST001") 
// Expected: ACTIVE with warnings 
GetTestStatus("ST002", "TEST001") 
// Expected: PAUSED (due to HIGH severity violation) 
// Generate Proctor Report 
GenerateProctorReport("TEST001") 
// Should list all violations by all students in the test

You have to design and implement a logger library that applications can use to log messages. Clients/applications make use of your logger library to log messages to a sink.

Platform Capabilities:

• Message:
  • Has content which is of type string.
  • Has a level associated with it.
  • Has namespace associated with it to identify the part of application that sent the message.
• Sink:
  • This is the destination for a message (e.g., text file, database, console, etc.).
  • Sink is tied to one or more message levels.
• Logger library:
  • Requires configuration during sink setup.
  • Accepts messages from client(s).
  • Routes messages to appropriate sink based on the level.
  • Supports following message level in the order of priority: FATAL, ERROR, WARN, INFO, DEBUG. Message levels with higher priority above a given message level should be logged. Ex: If INFO is configured as a message level, FATAL, ERROR, WARN and INFO should be logged.
  • Enriches message with additional information (like timestamp) while directing message to a sink.
  • Should not impact the application flow.

Sending messages:

• Sink need not be mentioned while sending a message to the logger library.
• A message level has a 1:1 mapping with sink.
• Client specifies message content, level and namespace while sending a message.

Logger configuration (see sample below):

• Specifies all the details required to use the logger library.
• One configuration per association of message level and sink.
• You may consider logger configuration as a key-value pair.
• Example:
  • logging level
  • sink type
  • details required for sink (e.g., file location)

Bonus Capabilities:

• No information loss. Logger library should log all the messages before the client application shuts down.
• Log Level for the application can be updated dynamically.

Given a list of locations, where each location is represented by a list of regions from specific to general (e.g., ["Bengaluru", "Bellandur", "Marathahalli"]), find the smallest area (region) that contains both Area1 and Area2.

Example:
Input:
Locations = [["Bengaluru", "Bellandur", "Marathahalli", "Kormangala"], ["Karnataka", "Bengaluru", "Mysuru"], ["Maharashtra", "Mumbai", "Pune"], ["India", "Karnataka", "Maharashtra"], ["Italy", "Rome", "Venice"], ["World", "India", "Italy"]]
Area1 = "Bengaluru"
Area2 = "Pune"

Output:
Smallest area containing Area1 and Area2: "India"
LCA problem :)

Allen has a few classes, each with a certain number of students and a given pass ratio (number_of_students_passed / total_number_of_students_in_class). New students need to be admitted in a way that it maximises the pass ratio for Allen.

Design AllenFit, a platform very similar to cult.fit. The discussion covered various aspects of the system:

• Detailed discussion of data models.
• High-Level Design, exploring both Monolith and MicroService architecture approaches.
• Definition and discussion of API signatures.

I was tasked with designing an entire Vaccination Booking System within 100 minutes. The interview included an initial and final 10-minute discussion period, leaving me with 100 minutes to both conceptualize and code the system. The interviewer provided a specific set of requirements, for which I needed to create APIs/functions. The main requirements were:

1. Add users and vaccination centers.
2. Allow each vaccination center to have varying daily capacities, be located in different districts and states, and support modification/addition of daily capacity.
3. Enable retrieval of a vaccination center's capacity for any given day.
4. Provide a list of all vaccination centers within a specific district.
5. Allow users to book a vaccination slot, returning a booking ID and decreasing the center's capacity. This also involved checking if the user is above 18 years of age and if the center has the required capacity.
6. Allow users to cancel their booking using the booking ID, which should also free up the center's capacity.

You are a budding entrepreneur who devised an idea to build an e-commerce giant like Amazon, Flipkart, Walmart, etc. As part of this ambition, you want to build a platform to duplicate the concept of Limited Time Deals.

Limited Time Deals

A limited-time deal implies that a seller will put up an item on sale for a limited period, say, 2 hours, and will keep a maximum limit on the number of items that would be sold as part of that deal. Users cannot buy the deal if the deal time is over. Users cannot buy if other users have already bought the maximum allowed deal. Users can buy up to one item as part of the deal.

The task is to create APIs to enable the following operations:

• Create a deal with the price and number of items to be sold as part of the deal
• End a deal
• Update a deal to increase the number of items or end-time
• Claim a deal

Guidelines

• Document and communicate your assumptions in README.
• Create a working solution with production-quality code.
• Use an external database like Postgres/MySQL or any NoSQL database
• Define and Create APIs to support the operations mentioned above
• Write a few unit tests for the most important code

What are we looking for?

• Your approach to the solution
• How you write code in terms of readability and maintainability
• Usage of best practices
• Testing skills

Design Book My Show system (HLD & LLD). Address how to handle concurrency. Define all entities and relationships among them.

Given an integer array nums, return all the triplets [nums[i], nums[j], nums[k]] such that i != j, i != k, and j != k, and nums[i] + nums[j] + nums[k] == 0. Notice that the solution set must not contain duplicate triplets.

Given an array of intervals where intervals[i] = [starti, endi], merge all overlapping intervals, and return an array of the non-overlapping intervals that cover all the intervals in the input.