I needed a CAPTCHA generator for some stuff I’ve been doing. I looked around and did find some assemblies for .NET. I thought of coding my own CAPTCHA generator and decided to do this using C#. The result – You can download/contribute here. You can even download a sample usage of this in a Windows Forms application form the “Releases” section. This can even be used in ASP.NET applications. This assembly will need permission to write to disk (to store the CAPTCHA image generated).

Usage

using CAPTCHA;
CaptchaGenerator cgen;

Single custom coloured CAPTCHA
cgen.CaptchaColor = Color.FromArgb(130, 120, 130);
CaptchaText = cgen.GenerateCaptcha(@”G:\test1.gif”);
pictureBox1.ImageLocation = @”G:\test1.gif”;

Default Random Coloured CAPTCHA
cgen.ResetCaptchaColor();
CaptchaText = cgen.GenerateCaptcha(@”G:\test1.gif”);
pictureBox1.ImageLocation = @”G:\test1.gif”;

What is an anagram?

Problem: Given a file containing words, re-arrange it such a way that all anagrams appear consecutively.

Example:
Given,
dcba
pqrs
zyx
cbad
xyz
sqrp
abcd

The result should be:
abcd
cbad
dcba
pqrs
sqrp
xyz
zyx

Here is a simple Perl + unix command line which does the job:

#!/usr/local/bin/perl -w

use strict;

open(INP,$ARGV[0]);

while(<INP>) {
   chomp;
   my $sig = join ”, sort split(”,$_);
   print “$sig\t$_\n”;
}

Command line: ./anagram.pl ip.txt | sort | awk -F’\t’ ‘{print $2;}’

Technique: Every word is associated with a signature. Here, a signature is nothing but the word with all the characters in it appearing in sorted order.

Here is how it looks:

abcd    abcd
abcd    cbad
abcd    dcba
pqrs    pqrs
pqrs    sqrp
xyz     xyz
xyz     zyx

Then, awk -F’\t’ ‘{print $2;}’ simply prints the original words (column 2).

I’ve been downloading software from my MSDN Subscription account. MSDN provides a custom download application which (un)fortunately does not have the feature to schedule downloads to begin at a particular time. Also, I’m not allowed to use DAP or any other download accelrator to download from MSDN. Sharath had pointed me to this sometime back. PTFB is a trial version software, so, here is a free version of a similar (but much more simpler, lesser features & less jing-bang) application which does the same job. I’ve called it Click-O-Matic (for the lack of a better name )

A ”just-works” version is ready. In case you are intrested to use this, leave a comment here with your e-mail ID and I can mail the setup file to you.

For the geekier ones here, I wrote this in C# using simple PInvoke to simulate the mouse clicks.

After hunting around for a way to get internet connectivity on my WM 5.0 PPC Emulator, I came across an informative thread on MSDN Forums. The two suggestions given there didn’t work for me. Unfortunately the PPC Emulator cannot be cradled in Vista’s Mobile Device Center yet, which is sad. When is a fix coming for this? I hope I won’t have to wait for Orcas. [Ref: VSD team blog]

Many a times I have come across scenarios where I have to read from a pipe in my Perl script. It is scenarios where I zcat from a file into my program -

$ zcat myfile.gz | ./myscript.pl > dump.txt

This can be done pretty easily:

while(<>) {
# $_ is a special variable that stores the current line read
# Here, my field seperator is ^A
@fields = split(/001/,$_);

$_ = <>; # Read the next line, for whatever reason
if($_) {
print $_;
}

# Do anything else here
}

If you are impressed with what Doug Cutting’s Lucene can do to your data, to enable super-fast searching, then, you can will be happy to know the existence of Plucene (a Perl port of Lucene). Off late I have been playing around with Plucene, indexing GBs of data, which I will have to query in a tight loop later.

So, why Lucene? Lucene stores data in the form of an inverted index which makes retrieval significantly faster compared to a normal indexing scheme.

A very simple example scenario where we have 3 documents containing different words. This is how a normal indexing scheme and an inverted index would index this data-

Normal Index
Doc1 – Bill Gates, Linus Torvalds, Richard Stallman
Doc2 – Steve Jobs, Scott Mc Nealy, Linus Torvalds, Bill Gates
Doc3 – Bill Gates, Steve Jobs, Larry Ellison, Scott Mc Nealy

Inverted Index
Bill Gates – Doc1, Doc2, Doc3
Linus Torvalds – Doc1, Doc2
Richard Stallman – Doc1
Steve Jobs – Doc2, Doc3
Scott Mc Nealy – Doc2, Doc3
Larry Ellison – Doc3

It is quite clear that a search for “Bill” on the inverted index will right-away return the documents in which the term appears. Whereas, in the case of a normal index, we’ll have to go through all the documents and check if the search term exists.

use Plucene::Document;
use Plucene::Document::Field;
use Plucene::Analysis::SimpleAnalyzer;

# Use the simple analyzer to tokenize the input in the default way
my $analyzer = Plucene::Analysis::SimpleAnalyzer->new();

# Create an object of Index::Writer which will write into the index
$writer = Plucene::Index::Writer->new(“/usr/local/my_index”, $analyzer, 1);

my $DocToIndex;
open(DOC, $DocToIndex);

# Create a new Document object, which will contain the fields & corresponding values
my $doc = Plucene::Document->new;

while(<DOC>) {
# Read from the file
my $line = <DOC>;
# Create a text field and store a unique ID in it. Generation of ID not shown here.
$doc->add(Plucene::Document::Field->Keyword(“id” => $id));
# Create a text field and store each line of the file in it
$doc->add(Plucene::Document::Field->text(“text” => $line));
}

# Add the document to the present index
$writer->add_document($doc);

# Merge multiple segment files created while indexing
$writer->optimize;
undef $writer;

Plucene would have now created many files in /usr/local/my_index which together forms the index. The purpose of contents of each file is described in http://lucene.apache.org/java/docs/fileformats.html

Next, let’s see how we can query this index.

my $parser = Plucene::QueryParser->new({
analyzer => Plucene::Analysis::SimpleAnalyzer->new(),
default => “text”
});

# Prepare the query – search for Bill in the text field
my $query = $parser->parse(‘text:”Bill”‘);

# Which index to search?
my $searcher = Plucene::Search::IndexSearcher->new(“/usr/local/my_index”);

my @docs;
# A callback which is called every time a search hit is found.
my $hc = Plucene::Search::HitCollector->new(collect => sub {
my ($self, $doc, $score) = @_;
push @docs, $searcher->doc($doc);
});

# Search!
$searcher->search_hc($query, $hc);

# @docs contains Document objects, so, extract only the IDs from it by mapping it to a @results array
my @results = map {
$_->get(“id”)->string;
} @docs;

# Print the ID of the documents which contained the search term
foreach my $id(@results) {
print “\nRes: “, $id;
}

This is a very simple implementation of Plucene. However it is highly scalable and many more complex applications can be built to make use of Plucene.

I came across a situatuion to very simply join 2 files on my machine, wherein one is a huge gzip file (16GB after compression) and the other is flat text file. Unzipping the .gz was not a good idea. So, I had to zcat the .gz and pipe it into a the join command to get my job done. The join command requires both the file names to be specified and does not allow something like:

$ zcat myfile.gz | join myotherfile.txt

It expects the command to be used as:

$ join file1 file2

I was too lazy to write a Perl script or even awk code to do this. Given that I have been using Unix extensively only recently, I didn’t know that some commands allow you to do this:

$ join file1 -
where, “-” means- take the input from the standard input.

That solves my problem!

All I did was:

$ zcat myfile.gz | join myotherfile.txt – > output.txt

Wow, only now I realized that Raj has mentioned my name in the context of his book which is titled – “Let’s Build A Compiler For The CLR“. Thanks Raj! His book is a wonderful piece of writing. Raj has struck a very nice balance between the geek-ness and simplicity. Do read it if stuff like Compilers fascinates you.

Many people (including me) have faced the issue of connecting to a webservice from a Windows Mobile 5.0 emulator. The error generally encountered is- “Unable to connect to network”.

I was able to overcome this problem after learning from this post that I need to cradle¹ the emulator and then deploy the application. Before you cradle the emulator, make sure you have a compatible version of ActiveSync running on your machine. Configure your ActiveSync to connect using DMA (because the intention is to connect to the emulator).

I used my desktop’s IP address (and not “localhost”, nor the machine name) to add the webreference (of the webserivce) in the mobile device project.

Rest of the steps in cradling the emulator is neatly laid out in this post.

Note:
1. To cradle your emulator, first connect to it using the Device Emulator Manager, only after which the “Cradle” option in the Actions menu will be enabled.

Soon after Imagine Cup 2006, India concluded, with Italy taking home the cup for the Software Design invitational (Photographs), Microsoft announced the theme and the venue for Imagine Cup 2007. Korea would be hosting this mega-event in 2007. The theme being:

“Imagine a world where technology enables better education for all”

Frankly, the theme of IC ‘06 (Imagine a world where technology enables people to live healthier lives) didn’t appeal to me, but, this one is really good and equally interesting. In addition to the invitationals present in IC ‘06, Imagine Cup 2007 will have 3 (not completely ‘brand’) new invitationals- Web development (was there in 2005), Embedded development (probably Windows Embedded Challenge merged into IC) and Photography (wow! If time permits, I’d love to get clicking with my Canon S2 IS).

Good luck to all those of you getting ready to rock!

Note: My first blog post from Windows Live Writer. It rocks! Yes, it does.