Orestes Carracedo

Scrum Master, PHP Ninja, cat owner
14 January 2015

I've been entering Facebook's Hacker Cup for a few years now. Some years I've gotten past a couple of rounds, others I haven't done so well. Anyways, I really like participating and I decided to share my setup.

I use the same structure for every problem so I can be more efficient. Every problem:

  • Is in a directory named using the point value and the problem name, like 30 Balanced smileys.
  • Contains a readme file with the full description of the problem.
  • Contains an example directory with the input and output files provided in the problem description.
  • The data directory contains the generated input provided for the submission.
  • The generated directory contains the output generated for the submission.

The tight loop

I'm using the simplest quickest feedback loop I could come up with:

  1. Run the program piping in the input from the example file and piping out the output to an output file.
  2. Diff the generated output file against the expected output file.
  3. Repeat

An example using php:

watch -n 1 "php solve.php < example/input.txt > output.txt && diff example/output.txt output.txt"

Using python:

watch -n 1 "python solve.py < example/input.txt > output.txt && diff example/output.txt output.txt"

I usually have this running in a session, and code in a different one. I like running the code very second and not relying on file watchers

What I often do wrong

This time I entered the qualifying round the last day. I ignored my calendar events for the day when I shouldn't. As a result, I entered the round feeling in a hurry and didn't concentrate as much as I should've.

In past editions I've overlooked the constraints and tested the code using simple scenarios. The problem comes when the generated input hits the constraint limits and my code is not optimized at all, taking a lot of time to perform the calculations and making me fail the problem.

Another mistake I made was preparing only one problem. Chances are I'm going to be fail to think about every scenario and fail the problem. Solving (or at least trying to) all the round's problems should always be the way to participate.


Categories: programming