Fora Travel Software Engineer Interview Experience — Coding, System Design, and API Design in One Technical Screen

Coding

The question was pretty simple:

Q: Given two unsorted integer arrays a and b, where a has enough placeholder positions at the end to hold all elements of b, merge b into a and sort the final array in ascending order.

Example:

a = [5, 1, 3, 0, 0, 0]
b = [6, 2, 4]
result:
a = [1, 2, 3, 4, 5, 6]

Additional constraints:

• Both a and b are unsorted
• a has enough placeholder positions at the end to hold b
• The final result needs to be placed in a
• There was no explicit requirement that you couldn't use extra space / had to be O(1) space
• The final result needs to be in ascending order

System Design

Q: Design a system where a user's mobile app periodically sends their location to the server, and the system sends a notification message to all users within a given radius x.

Things to consider:

• The mobile app periodically sends its location
• The server receives and saves the user's latest location
• Given a latitude/longitude and a radius x, find nearby users
• Send a notification to all users within radius x
• How often locations get updated
• Real-time requirements for notifications
• Scalability when a large number of users update their location at the same time
• Location data expiring / stale data
• Notification delivery

Things you could clarify further during the interview:

• How often does a user's location update?
• What's the latency requirement for notifications?
• Roughly what range is x?
• Roughly what's the user scale and location-update QPS?

API Design

There were three pages, and I needed to design the corresponding APIs.

Page 1 — Course List
Shows all courses, and whether each course is completed.
For example, it needs to return:

• Course ID
• Course Name
• Completed

API: GET /courses

Page 2 — Module List
After the user picks a course, show all modules under that course, and each module's completion progress.
For example, it needs to return:

• Module ID
• Module Name
• Completed Lessons
• Total Lessons
• Progress

API: GET /courses/{courseId}/modules

Page 3 — Lesson List
After the user picks a module, show all lessons under that module, and whether each lesson is completed.
For example, it needs to return:

• Lesson ID
• Lesson Name
• Completed

API: GET /modules/{moduleId}/lessons

If the pages support the user updating completion status, you also need a corresponding update API, for example:
PUT /lessons/{lessonId}/completion

For each API you needed to spell out:

• Request parameters
• Request body (if any)
• Response format
• Authentication / user identity
• Error response

Overall impression: Coding was pretty simple; System Design leaned toward location + geospatial query + notification; API Design was the fairly common Course → Module → Lesson three-tier structure.