Pi Zero, 2p for scale, not included with prize.
Last week we started a competition to win a Pi Zero. We’ve had a small number of entries, half from school age people eligible to win, the other half from entertained techies. We’ve also been using this as a job filter for some time so we have a rich depth of existing answers.
The competition is very simple, our web-page generates a mathematical sum for you to work out the answer to, and in order to succeed you have to send us the answer within one second. It’s an anti-turing test – a person can’t do it but a computer can. When you’ve succeeded we ask you to send us the code. This gives two important things, a code sample that a candidate wrote and an idea of how long it took them to work out they should automate it.
A text-book answer from an experienced techie is about 15-30 minutes and delivers a short piece of code that fetches the web-page, finds the sum with a regexp or similar, works out the answer with eval, creates the response and sends it back to us. However, people are much more creative than that.
One excellent answer was a single line of shell script, which did the whole thing in bash, but even more cleverly searched the process list for the command that had been typed in, added the escaping back in and then mailed itself to us – a one liner that did the puzzle, recreated its source code and emailed itself to us.
Another excellent answer was someone who guessed that our code had a 32 bit roll-over bug in, tried options until we generated an answer bigger than 2^32 and fixed the otherwise text-book code to implement the bug on our side.
The absolute worst answer we’ve ever seen was someone whose CV listed them as a professional programmer with five years experience. After two whole days of typing answers into the website they finally worked out that the problem had to be automated. After three days of development they wrote a vast piece of Java code that was able to download the page and find the problem but it was only able to work out the answer if there were only three numbers and they all had to be added together. Instead of improving the code for the general case they put it in a loop and repeatedly called the page until by sheer luck they got a page their code could answer. Creative genius but not in a good way.
On to the entrants
So this is a difficult challenge for school age children and teenagers. Most of the entries came from older children 16 and up, and it’s clear that it was difficult and they had to learn new things specifically to solve this. PHP and Python were the preferred languages – the most novice friendly of all the tools available. We were very torn as to who should win. After lots of deliberation our runner up is this php entry from Nils in Germany who was also the first to submit,
// That was fun. There should be more conetsts like this.
// Sorry for the incredibly hacked together code...
<?php
$challenge =
file_get_contents(‘http://sphinx.mythic-beasts.com/cgi-bin/job.pl’);
$task = preg_replace(‘/.*
Evaluate /is’, ”, $challenge);
$task = preg_replace(‘/ \, .*/is’, ”, $task);
$id = preg_replace(‘/.*name=\”id\” value\=\”/is’, ”, $challenge);
$id = preg_replace(‘/\”.*/is’, ”, $id);
function calc_string( $mathString ){
$cf_DoCalc = create_function(“”, “return (” . $mathString . “);” );
return $cf_DoCalc();
};
$ans = calc_string($task);
$url = ‘http://sphinx.mythic-beasts.com/cgi-bin/job.pl’;
$data = array(‘answer’ => $ans, ‘id’ => $id);
$options = array(
‘http’ => array(
‘header’ => “Content-type: application/x-www-form-urlencoded\r\n”,
‘method’ => ‘POST’,
‘content’ => http_build_query($data),
),
);
$context = stream_context_create($options);
$result = file_get_contents($url, false, $context);
var_dump($result);
?>
Things we particularly like are that all the comments and code and email are in English to make it easier for us, even though it’s the authors second language.
Our winner though goes to 13 year old Nick. From a pure technical standpoint his code isn’t as good as Nils’ entry above, but through the comments it tells the story of slowly working his way towards the solution and appropriately credits the help he received – both personal and online.
#Mythic Beasts - Win a Pi Zero
#Written by Nick Lockhart from Chepstow, Wales, aged 13 3/4
#with help from an old fossil (his dad)
#You will need LXML for Python and Requests
from lxml import html
import requests
debugmode = 1
#get the page and parse all
elements into a Python list.
#For this purpose we should only get one element.
page = requests.get(‘http://sphinx.mythic-beasts.com/cgi-bin/job.pl’)
tree = html.fromstring(page.content)
paragraphs = tree.xpath(‘//p/text()’)
#Split out the question.
#First take out everything after the sum (space included)
#And then remove everything before the sum (space again included.)
#And convert to a string. Oddly, after the second time, we have to
reference the second element as there is a blank string in question[0]
#Finally, evaluate it.
question = paragraphs[0].split(‘ ,’)
question = question[0].split(‘Evaluate ‘)
question = question[1]
answer = eval(question)
if (debugmode == 1):
print(“The question was: ” + question)
print(“The answer should be: ” + str(answer))
#There’s a hidden input labeled “id”, which seems to be randomly generated.
#This is probably to track who’s submitting.
#We will also need to extract this.
#I learnt this piece of magic with help from StackOverflow. Thanks,
Mathias Muller!
secretkey = tree.xpath(‘//input[@name=”id”]/@value’)[0]
#That’s all we need to POST. Let’s generate a payload, send it off and
extract the response.
#The server expects the answer to be a string, so we convert it to a string.
payload = {“answer”:str(answer),”id”:secretkey}
if (debugmode == 1):
print payload
response =
requests.post(“http://sphinx.mythic-beasts.com/cgi-bin/job.pl”,
data=payload)
responsetree = html.fromstring(response.content)
print(responsetree.xpath(‘//p/text()’))
Of course the final comment to everyone who entered is if you ever need any kind of hosting, domain name or similar send us an email and include your entry number for a freebie / upgrade /discount. Secondly if you seek summer work or gap year employment, we’d invite you to get in touch and we guarantee that we’ll read your CV and take your application seriously.
