UnderGround System

An underground railway system is keeping track of customer travel times between different stations. They are using this data to calculate the average time it takes to travel from one station to another.

Requirement

Implement the UndergroundSystem class:

• check_in(id, station_name, time)
  • A customer with a card id, checks in at the station station_name at the time.
  • A customer can only be checked into one place at a time.
• check_out(id, station_name, time)
  • A customer with a card id, checks out from the station station_name at the time.
• get_average_time(start_station, end_station)
  • Returns the average time it takes to travel from start_station to end_station.

Notes

1. The average time is computed from all the previous traveling times from start_station to end_station that happened directly, meaning a check in at start_station followed by a check out from end_station.
2. The time it takes to travel from start_station to end_station may be different from the time it takes to travel from end_station to start_station.
3. There will be at least one customer that has traveled from start_station to end_station before get_average_time is called.
4. You may assume all calls to the check_in and check_out methods are consistent.
5. If a customer checks in at time t1 then checks out at time t2, then t1 < t2.
6. All events happen in chronological order.

Input

Commands file:

• check<in/out>,id,station_name,time
• get_average,start_station,end_station

Example

check_in,45,Leyton,3
check_in,32,Paradise,8
check_out,45,Waterloo,15
check_out,32,Cambridge,22
get_average,Paradise,Cambridge

Output

Paradise,Cambridge,14.0

Example 1

Input

check_in,45,Leyton,3
check_in,32,Paradise,8
check_in,27,Leyton,10
check_out,45,Waterloo,15
check_out,27,Waterloo,20
check_out,32,Cambridge,22
get_average,Paradise,Cambridge
get_average,Leyton,Waterloo
check_in,10,Leyton,24
get_average,Leyton,Waterloo
check_out,10,Waterloo,38
get_average,Leyton,Waterloo

Output

Paradise,Cambridge,14.0
Leyton,Waterloo,11.0
Leyton,Waterloo,12.0

Implementation

Notes

Assumptions

• I am assuming there was a typo in the Example 1 Input and I've changed one of the lines from check_in,10,Waterloo,38 to check_out,10,Waterloo,38
• This solution is over-engineered for such a simple problem to solve, however, I've decided to use Ruby and Kafka to solve this code assessment since I know these are the technologies used by the team and as a way to demonstrate proficiency on the confluent's tech stack

Decisions to reduce scope

• The setup to run kafka is not configured to be highly available and in a real production environment this needs to be configured differently
• I've decided to not use Ruby on Rails in order to reduce some framework dependencies given the reduced scope of this problem
• The KSQL query to calculate trips average time can be way more performant and further optimisations could be applied incremental-averaging

Executing unit tests

rspec

Executing integration tests

./scripts/test-integration.sh

Dependencies

• Ruby 3.0.2
• Bundler
• Docker
• gettext

To install gettext on Mac OS X with brew execute brew bundle in this directory or just brew install gettext