How I found a bug in HackerEarth


I am not a competitive programmer. I love programming, but more so I love building things. As a result, I rarely participate in coding contests. Even when I do, I try to use languages like Ruby and Python just to see if I can do it my way, so to speak.

While trying a contest in Ruby, I realized that I could not use the ruby prime library. This is a standard library in Ruby for a long while, and HackerEarth platform runs on 2.1.1, which is quite new.

I reported this as a bug to HackerEarth in September ‘14. A quick reply from HE made me realize that they weren’t understanding the issue:

Modules like mathn or erb are part of standard library. They are available.

Try using, require ‘erb’require ‘mathn’ in code editor.
However 3rd party libraries are not available.

I decided to do some tests and check all standard libraries for their availability. For those unfamiliar with Ruby, this is how you load a standard library in ruby:

require 'prime'

Using the HackerEarth API, I was able to write some quick code that tested all expected libraries:

while read lib; do
  echo "Testing $lib"
  curl -s -d "client_secret=API_SECRET&lang=RUBY&async=0&source=$SOURCE" > $lib.json
done < libs.txt

Here libs.txt contains a list of all standard libraries. The above code is in bash, and makes use of curl. Parsing the results, I replied with the following:

Requiring the following libraries raises a missing error:

coverage - RE
extmk - RE
fiddle - RE
io/console - RE
json - RE
minitest - RE
minitest/benchmark - RE
minitest/spec - RE
mkmf - RE
objspace - RE
prime - RE
psych - RE
racc - RE
rake - RE
rdoc - RE
rexml - RE
rinda - RE
ripper - RE
rubygems - RE
tk - RE
win32ole - RE
xmlrpc - RE

HackerEarth admitted the issue (I posted code to replicate on github), and have since worked on it. I just ran the tests again, and only the following libraries are unavailable now:

curses - RE
dbm - RE
debug - RE
extmk - RE
gdbm - RE
generator - RE
iconv - RE
racc - RE
readline - RE
rexml - RE
rinda - RE
tk - RE
win32ole - RE

A few of these are understandable (win32 since HE platform runs on Linux, and tk, which is a graphical library). A few of these are unavailable in Ruby 2.1.1 (I copied the list of libs from the 2.1.3 docs).

Kudos to HackerEarth for fixing a bug that very few of their users would have faced. All the source code for this post can be found at github.

Note: This article was copied from HackerEarth because they are shutting down their notes platform.

Published on February 12, 2015