Good bye Heroku !

I primarily work on Ruby on Rails and I use to deploy one of my pet projects to Production entirely on the Heroku's free tier. It was a wonderful two years to see having my application running there during which time I had around a thumping 10 Million page views! Heroku's free tier is one of the most used around the world for quickly showcasing development applications. However, my Production application was such that all my needs felt well under Heroku's free tier.

Here are some of the freebies I use to enjoy

• Free Dedicated (techincally not) machine with 512 MB - The reason its technically not because you are allotted a free worker that would go to sleep if the application is not up for 30 minutes. However you could easily overcome this with something like Pingdom.
• Free Postgres Database - Although there was no specific size limit to this other than a maximum number of 5000 rows, I would still say this is one of the best things Heroku offers. Not only your application can talk to it, anything anywhere from the world can talk to the database directly. And that too 100% free!
• Free emails via Sendgrid - A maximum 200 emails per day! Sendgrid's free Addon allows me send upto 200 emails per day. My application's requirement was in the range 20-40.
• Unlimited Job Schedulers - Although they would take one entire and the only worker allotted to you to spin, this is a boon considering you do not have a full fledged linux machine with you. I use to have only one rake task that takes a routine back up of my data as CSV and email it to me.
• Free PG Backup - Again, if you want to routinely backup your data, you don't have to write any complex code. Heroku provides this out of the box and for free!

Now that Heroku is pulling down the curtain on the 24 hour availability or to pay $7 a month, I have no other option to switch to a much better alternative - that is Digital Ocean. Sign up here for a free $10 credit - https://m.do.co/c/21693a3f9c9e

Sad to depart ways, but you made me learn a lot of stuff in these two + years.

Cheers!
Braga

My first ruby gem horoscope is live

I wanted to write a rubygem on my own for a long time. Never had the time really to write one. However, recently I had some spare time during which I wrote this gem called horoscope. This gem will help drafting the horoscope of a person given the birth date, time and the place. Source is hosted at Github. As with every other open source project out there, feel free to fork it and add more to your liking

Screenshot at Github

Proud to release this and I am planning to add more features to this. Also, planning to release different gems. If you want something particular or specific, don't be shy, add it in the comments section and I would be more than happy to contribute!

Cheers!
Bragboy

Tree Traversal in C++

We've already seen many implementations of tree and its uses in java. Lets look at a simple implementation of traversing on a tree in C++. Code has been given below which I think is quite self descriptive.

Regards,
Jack

Write a program to find the number corresponding to a alphabet and vice-versa with the given rule

Problem:
A = 1
B = A*2 + 2
C = B*2 + 3...
1. Write a program to find the number corresponding to a alphabet and vice-versa.
2. Given a series like GREP find the total in numbers. Given a number like 283883, find the shortest alphabetical series corresponding to it.
Compute above recursively when required and do not pre-compute and store beforehand.

Solution:
The solution is straightest-forward. Java code given below.

Cheers!
Braga

Write a program to build a small knowledge base about top "N" movies listed at IMDB

This was an interesting problem that I came across with. This problem is like an open book exam and race against time. The problem had to be solved within an allocated amount of time with a technology stack that is limited only to Ruby/Python/Node.js/Perl.

Few googling here and there and with some knowledge about Ruby I was able to solve this problem within an hour.

Problem Statement:

Build a small knowledge base about top "N" movies listed at http://www.imdb.com/chart/top. Each movie should mention the cast written on the individual page of the movie.
Given the name of a cast member, you should be able to return the movies out of the top "N" movies he/she has acted in. "N" will be passed by the user.
The knowledge base should be built during the runtime and stored in a data structure of your choice.
Q1. For example, if N=3, then you should parse the first 3 movies' individual pages from that page (http://www.imdb.com/chart/top) and build the knowledge base of the cast (there are about 15-20 on every page). Upon querying for "Morgan Freeman", you should return "The Shawshank Redemption". Do not use any external api for this.
Use only Ruby/Python/Node.js/Perl.

Solution:


Cheers!
Braga

Novel finder Program

This was one of the problems that I had faced during one of my interviews. The problem sounded interesting and I was given 1 hour to solve it which I did quite comfortably.

Problem:

The K-doublets of a string of characters are the ordered pairs of characters that are K distance from each other. A string is K-singular if all its K- doublets are different. A string is Novel String if it is K-singular for all possible K distances.

For e.g. take the string FLBL, its 0-doublets are FL, LB and BL. Since all these are different, FLBL is 0-singular. Similarly, its 1-doublets are FB and LL, since they are different FLBL is 1-singular as well. Lastly, the only 2-doublet of FLBL is FL, so FLBL is 2-singular. Hence, FLBL is a Novel String.

Note that the fact that FL is both a 0-doublet and 2-doublet is insignificant as zero and two are different distances.

Input:

The input is one or more non-empty strings of at most 100 capital letters, each string on a line by itself, followed by a line containing only two dollars ($$) signaling the end of the input.

Output:

For each input line, output whether or not it is a Novel string using the exact output format shown below.

Sample Input: (Input File: novel.in)

FLBL

FFLL

ORDINARY

R

QYQRQYY

$$

Sample Output: (Output File: novel.out)

FLBL is a Novel string

FFLL is not a Novel string

ORDINARY is a Novel string

R is a Novel string

QYQRQYY is not a Novel string

Solution:

To attack this problem, you first have to find all the doublets for each distance starting from 0 to the maximum distance which would string's length minus one. Then keep pushing them into a hash set. Whenever the add() method of the Set returns false, it means we are adding a duplicate hence, its not a Novel text. Here is the Java source code.


Cheers!
Braga

Windows Phone 7.5 - Home button Navigation and Exit Confirmation

While developing a windows phone application, the one which involves navigation to various pages starting from something called as a homepage would quickly become annoying. You will find yourself in deeper pages and as a means on coming back to the home page, you will keep pressing the back button so many times it will exit you out of the application.

There are couple of problems associated with this. The user is forced to keep in mind how deep he has in the navigation page. The other main problem is he will not have patience to wait to go to the home page and pressing the back button on the first page will obviously throw you. This is because the navigation details are stored in a stack.

It is always nice to provide a home button to the end user on all the pages so that on click of them will take it to the home. Also, you can always have a confirmation dialogue fired while exiting the application. First problem first.

This code armed with a Home button will do the job cleanly for you.

private void Home_Click(object sender, System.Windows.RoutedEventArgs e)
{
    int depth = NavigationService.BackStack.Count();
    for (int i = 0; i < depth - 1; i++) { NavigationService.RemoveBackEntry(); }
    NavigationService.GoBack();
}

The funda here is it will empty all the stack and will call the back action of the navigation service just once making sure that the next back() will empty the stack and will make you quit.

As I told before adding this code to the MainPage.xaml.cs will show a confirmation popup while quitting the application so that user only deliberately quits but not accidentally.

protected override void OnBackKeyPress(System.ComponentModel.CancelEventArgs e)
{
    if (MessageBox.Show("Are you sure you want to exit?", "Exit?", MessageBoxButton.OKCancel) != MessageBoxResult.OK)
    {
        e.Cancel = true;
    }
}

These techniques are very simple and subtle but will improve the usability of your application by leaps and bounds.

Cheers!
Braga

Windows Phone 7.5 WebBrowserTask - Simple Yet Powerful

WebBrowserTask is one of the most simple yet powerful tasks I found in Windows Mobile development. It is amazingly simple, just two or three lines of code and super tempting to include it in your project. Lets quickly see how to use it and places where you can utilize its capability at the presentation level.

Enough intro, here is the code

WebBrowserTask pptTask = new WebBrowserTask();
pptTask.Uri = new Uri("http://www.iasted.org/conferences/formatting/presentations-tips.ppt");
pptTask.Show();

Damn simple isnt it? You could use this in places where you need to launch or open an URL in the inbuilt Internet Explorer. And the best thing about this is it will automatically detect the attachment file types (most of them) and opens them cleanly. For example, it could read ppt, pdf, xls even videos and open them cleanly. You can make the integration look rich by providing a button in the Application bar. Following is a screenshot.

Besides opening simple URLs consider using this Task to open regular attachments and make your end application look extremely rich with just one or two lines of code.

Cheers!

Braga

Windows Phone 7.5 - ShareStatusTask's Limitations

The Microsoft.Phone.Tasks namespace in Windows phone 7 is a neat way to access the default phone specific tasks. One such task is the ShareStatusTask. If you want to say share your status on facebook or twitter or to windows live account, you can do it in one shot.

The code looks very simple,

Very cool isnt it. But the usage of this kind of limited. You will have to have all the accounts configured already in your phone settings. I was looking for a direct solution to just provide a way to tweet. But it was not possible to tell the ShareStatusTask to open it only if it has Twitter. I had asked this question in Stackoverflow only to double confirm the above said point. This feature is not available in Emulator, hence posting a screenshot from a real device.

Anyways, this is one of the cool tasks available and just two to three lines will add social feature to your App, so do add it whatever be the case.

Cheers!
Braga

Windows Phone 7.5 - Rating/Review control Packages

There was a simple specification in my application that needs to have a Review feature. I started off with Google, but the irony here is the keyword "ratings" or "review" accompanied with Windows Phone 7 did not return results that I've been looking for. Instead it was returning the features and real reviews written for Windows Phone 7. The catch here was to convert my keyword to star rating control. I found some decent resources which are implementable, let me summarize them.

1) Silverlight Star Rating Control - This had most of the meat I was looking for. It was actually designed for silverlight and not really tested in Mobile or I can put it like I was not able to find snippets for Mobile implementation. However, it worked alright. The problem was that this package was not having a mechanism to NOT have the Half-Star Mechanism. Going through the source code confirmed that and I do not want to build a new dll out of it and include it in my project. So gave this up. But I would highly recommend this for web client.

2) The next one I stumbled upon was from a guy Jani Nevalainen. He has blogged it in his website and it had what I needed. But since it was not on a codeplex site/github, and due to its lack of documentation or support I had to push it down the priority list. I have not tried this, but my gut says it will surely work.

3) Another one which really looked promising was from a blogger named Matthieu. I thought it had everything and even the source on Github and the demo project worked flawlessly. I was expecting for a library file so that I could include it in my project and breathe easily. Unfortunately, that was not something already available. Yes, I can go through the code and compile a source out of it. But I was really lazy to do so. Hence dropped it. But I have to say this was a really good and careful implementation. Kudos to the Author.

4) And the winner was Coding4Fun! The most sexy and the most famous library for the Windows phone 7.5. It has everything and the forums are really great! Every week you can see builds coming and they are very much responsive to the features that you are suggesting. I could not say that this is the Open source folks' answer to Telerik, but this library is really good. I used their super slider to design my review page. I know it is not like the star mechanism, but still this did the job and it did really great for me!

Cheers!
Braga

Exception Handling in Windows Phone 7 - When all else fails

I was recently testing something with Toast Notifications with Windows Phone 7.1. Visual Studio that I use has amazing debugging features like any other IDE available IDE out there. Here was scenario. I need to send two types of Notifications Raw and Toast Notifications to my mobile and need to assert scenarios. Debugging the Raw Notification was very simple. However, I was not able to debug/step into when I launch the application after clicking the toast Notifcation.

It was really painful not to be able see any exception message. It was very annoying. Then I found a way to at least know what is happening. To do that, you can just go the App.xaml.cs file which has all the main entry and exit points to the application. To read more about this, just google life cycle of a windows phone app.

All I had to do was add a message box to the method Application_UnhandledException in the App.xaml.cs.

private void Application_UnhandledException(object sender, ApplicationUnhandledExceptionEventArgs e)
{
    MessageBox.Show(e.ExceptionObject.Message + "\n" + e.ExceptionObject.StackTrace);
    if (System.Diagnostics.Debugger.IsAttached)
    {
        // An unhandled exception has occurred; break into the debugger
        System.Diagnostics.Debugger.Break();
    }
}

Problem Solved. Now I could see the error messages/exception stack trace in a neat Message box!

Cheers!
Braga

Rails script/generate model with an association

I know this blog has been dormant for quite some days now for no apparent reason. But I would like to share what I learnt today. This is going to be in Rails (2.3.x) and hardly interest anyone who already knows it. But it still was a learning to me. I use to hate working in command prompt and was an IDE freak, a real good one too. But I was cornered to learn more on the command line front as well. Why waste an extra feather in the cap?
Bulling the shit, here is what I learnt today.

Rails has a script/generate ready for many usual stuff that we do. One of them is the model generator. It is not that much, but I was wondering whether it is possible to create associations using it. And I found it is not.

I tried a stupid model generation something like (in fact exactly like this)

rails -d mysql playground
cd playground
script/generate model project name:string has_many:tasks

It reeked,

exists  app/models/
exists  test/unit/
exists  test/fixtures/
create  app/models/project.rb
create  test/unit/project_test.rb
create  test/fixtures/projects.yml
create  db/migrate
create  db/migrate/20120227204200_create_projects.rb

My stupid assumption was that it would actually create a couple of models called projects and tasks. But to my wonder, it did not. The highlight was this command did not even raise any error. Inspecting the database migration, I found

class CreateProjects < ActiveRecord::Migration
  def self.up
    create_table :projects do |t|
      t.string :name
      t.tasks :has_many

      t.timestamps
    end
  end

  def self.down
    drop_table :projects
  end
end

And I did a migration and it did migrate without any errors. It silently ignored the line t.tasks :has_many. Not usual right?! But this is rails, you got to adapt and adapt very well. One more learning probably I could share are the commands that come with the script/generate model is the --pretend. This is like a dry run, does not actually creates a physical file but tells what its going to do. Thats it for today.

Cheers!
Braga

Reconstruct a binary tree given its Inorder and Preorder traversals in Java

This is one of the interesting problems that I encountered recently. Given two sequences one being an in-order traversed sequence and other being a pre-ordered traversed sequence, a binary tree has to be reconstructed out of it.

This is theoretically possible. This problem can be cracked if we form a common pattern between these two traversed values. In a pre-order traversal, the root element will always be the first element. This element when searched in an in-order traversal will have all elements to the left on the left side of the array and all elements to the right on the right side of the array.

Applying this solution recursively will give the binary tree for us. I have included a Swing UI so as to visualize the output easily.

Example,
Pre Order Sequence = A B D E C F G H I
In Order Sequence = D B E A F C H G I

I tweaked a bit from this source for UI.

The Node structure

The code for UI

Hope you learnt something today along with me.

Cheers!
Braga

Given a sorted array, find k in least possible time in Java

Given a sorted array and a value k, write a program to find whether that number is present in that array or not.

The first solution that comes to the mind for this problem is to traverse through the entire array and find whether it is having the value k and return true or false. This takes O(n) running time. But then, we are presented with a hint that the input array is sorted (lets assume in ascending order). This problem can be attacked by doing a divide and rule analysis.

This can be done recursively. See whether k is inbetween the last and first element in the array. If it is, then divide the array into two and repeat the same. If its not, simply return false. Yes, its as simple as that. Following is the java code for the same.

Leave some comments if you have anything to say.

Cheers!
Braga

Find middle element in a circularly sorted array

Given a circularly sorted array, find its middle element in best possible time.

A circularly sorted array is an array that is obtained by shifting an array k times. For example, the following is a circularly sorted array,

[5, 6, 7, 8, 9, 1, 2, 3, 4]

If you sort this array and find the middle element it will be 5. But then, sorting is a painful operation which will take O(nlogn) timing. So it is out of the equation right away. If you closely observe this problem, it is enough to find the shifting index, the place where the sorting varies. For example, the shifting index in the above example is 5.  Once that is found, then it is a matter of applying the bias over the length.

This program can be attacked in a recursive manner. Take the first and last elements in the array and compare them. If they are sorted, then the last element is greater than the first element. If this condition is not met, we will have to divide this array into two halves and try applying the same logic. If you do this, at some point you will arrive at a situation where you are left with only two elements or lesser. The end value is the shift index. Once the shift index is found, it is easy to find the middle element(s) for odd and even cases. Java code is below.

Leave comments if something is unclear.

Cheers!
Braga