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On-The-Beach-Coding-Exercise

Exercise for On The Beach to demonstrate coding, problem solving, and design abilities.

How to use

On the Beach specification demo

Run:

php demo.php

This should output:

Specification 1:
Input is: ""
Output is: ""

Specification 2:
Input is: "a => "
Output is: "a"

Specification 3:
Input is: "a => , b => , c => "
Output is: "a, b, c"

Specification 4:
Input is: "a => , b => c, c => "
Output is: "a, c, b"

Specification 5:
Input is: "a => , b => c, c => f, d => a, e => b, f => "
Output is: "a, f, c, d, b, e"

Specification 6:
Input is: "a => , b => , c => c"
Output is: "Job c. A job cannot depend on itself"

Specification 7:
Input is: "a => , b => c, c => f, d => a, e => , f => b"
Output is: "Job b. This job contains a circular dependency"

Command line utility

This is for inputting a custom job list as a string, and receiving a sequenced output.

php sequencer.php "job-list-here"

For example:

# php sequencer.php "a => , b => c, c => f, d => a, e => b, f => "

Job sequencer:
Input is: "a => , b => c, c => f, d => a, e => b, f => "
Output is: "a, f, c, d, b, e"

Tests

From inside the testing directory, run:

php phpunit.phar tests.php

Output should be similar to:

PHPUnit 8.3.4 by Sebastian Bergmann and contributors.

.....................                                             21 / 21 (100%)

Time: 133 ms, Memory: 10.00 MB

OK (21 tests, 51 assertions)

Initial Thoughts

  • Define class for jobs, and create object for each job
  • Each job should contain a reference to any dependencies and possibly dependents too
  • The job object should contain a marker to say whether it's dependencies have been resolved already or whether it is currently being worked on to help with circular dependency resolution
  • The job object should contain a marker to say whether it is already queued or not for the case of having multiple dependents, to prevent being queued more than once without having to search the queue
  • It's not specified in the challenge description, but it seems logical that a job may have multiple dependencies, so account for this using an array
  • Use an array to build the output sequence. While this case is computationally trivial, such an algorithm may be performance sensitive given a large number of jobs, so minimise expensive array manipulation where possible
  • Write tests to cover all cases in the given specification along with any extensions, and any testable units
  • Use PHP built in Exception handling for dealing with any errors encountered

Thoughts whilst working on it

  • Avoid making it unnecessarily complex
  • Don't really need any dependencies. Make it as easy as possible for me to run along with anybody who may be looking at it
  • Having the code run on a remote system means an annoying number of commits during testing and debugging
  • Jobs should have a "run" member function that checks all dependencies are resolved (have been run), runs the job if they are, and throws an error if not. It then sets a member variable to demonstrate the job has finished
  • Make a JobSequence class with a member variable of an array containing the Jobs to sequence, and member functions to sequence it
  • Look for jobs without dependencies and sequence them first. Not strictly necessary, but could be a performance gain for large, complex job lists
  • Used recursion to sequence jobs. For each job, the sequenced list was checked for a job's dependencies, and the job was added to the end of the list if it's dependencies were met. This was repeated until all jobs were added
  • Core functionality seems to be complete and working as per the tests
  • Does somebody need to be able to use the program to test it out? Make command line utility in sequencer.php
  • Make a demo to show that all specifications in the challenge are met in demo.php