K Palindromes puzzle

Here we have the K Palindromes puzzle from Javalobby:

You probably already know what a palindrome is: a string to results in the same word, whether read left to right, or right to left. A K Palindrome is when a string can be tranformed into a palindrome by changing K characters at most. Regular palindromes have K=0.

Your challenge today is to write a method which takes a string and a value for k and returns true if it the string qualifies as a K palindrome.

Below is the code in Ruby. Our input string is omississimo and it’s a 0 palindrome String.

The output is true. Do you have another solution? Drop your comments here!

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Minimum difference puzzle in Ruby

Folks, here we are for another puzzle from Javalobby:

Given two arrays, sorted and exactly the same length, write a function that finds a pair of numbers – one from each of the arrays – such that the difference between both is as small as possible.

Suppose our input arrays are [1,2,3,4,5] and [6,7,8,9,10]. Below is my solution in Ruby, it’s a one liner code :-):

The output is [5, 6].

Have another solution? Leave your comments here!

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Balancing arrays puzzle in Ruby

Here we are for another puzzle from Javalobby:

Given an array of numbers, return the index at which the array can be balanced by all numbers on the left side add up the the sum of all numbers of the right side.

For example, an array with [1,5,6,7,9,10] can be balanced by splitting the array at position 4

Here is the solution in Ruby:

The input array [1,5,6,7,9,10] will split the array at position 4, as stated above.

Any other solutions? Drop comments here ๐Ÿ™‚

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Finding the second highest frequency

It’s been a long time since I posted for the last time, but I promise I’ll try to keep this blog up-to-date ๐Ÿ™‚

One of the purposes of this blog is to explore new technologies and recently I’ve been studying Ruby solving some puzzles posted by on JavaLobby.

The problem is about finding the second highest frequency of a character in a String. Below is the Ruby code, using the powerful concept of Ruby closures.

For the input String "aabbbc", the result is "a". I could done it in a more OOP style, but I chose a more concise solution ๐Ÿ™‚

If you have another version in Ruby, feel free to post a comment!

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Undo svn add operation

If you want to cancel an svn add operation, do not use svn delete or svn remove, according to this post. You can issue the following command to undo a svn add:

svn revert --recursive your_folder

This tip was very useful for me today :-)

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Checkout only one file from Subversion

I was wondering how to checkout only one folder/file from SVN when I found this interesting tip. The command I issued to do it is the following:

svn co –depth empty

The above command checkout only one versioned directory, with its content empty. Now it’s possible to add other files and directories under the directory who was checked out.

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When to use TestNG or JUnit

There is an interesting discussion between using TestNG or JUnit on Java projects at Javalobby. It’s very worth reading.

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Some interesting Maven tips

Here are some Maven tips, extracted from Javalobby:

  • Maven rf option: If your project has some modules and the build fails at one of them, it’s possible to run the build only at this module, preventing from running the entire build. You can achieve this behavior by executing this command:
  • mvn -rf my-project clean install

  • Maven pl option: This option allows you to build specific modules instead of building all projects. You can execute the following command to have this behavior:
  • mvn -pl my-project-A,my-project-B clean install

    This command will build only my-project-A and my-project-B.

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Maven Eclipse plugin using project dependencies

Some months ago I was noting the behavior of the Maven Eclipse plugin during the eclipse:eclipse goal.

I realized that its default behavior is to build the dependencies based on the Eclipse projects instead of the installed packages on the repository. During development time, it’s the behavior we need, but if you want to build the Eclipse files using the packages on the repository, you have to use the following command:

mvn eclipse:eclipse -Declipse.useProjectReferences=false

By default, the useProjectReferences flag is set to true, in other words, the plugin will create and reference the projects in Eclipse. Without it you’ll have to use mvn install to make changes available for dependent projects. Very interesting to note.

Update *: After creating the project dependencies, you have to execute mvn install to make it available for mvn eclipse:eclipse on dependent projects for the first time.

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Configuration classes with Enums

As I mentioned on my previous post, an alternative implementation to create Singleton in Java is with Enum types.

Extending the idea, it is interesting to create classes which read configuration values from Properties files with Enum classes. Below is an example:

Configuration classes which read values from properties files should be Singletons that are loaded once on the application startup time.

The Configuration values can be used this way:

This example shows that the key and value from properties are stored with Enum constants. They are type-safe, they can be easily accessed through code completion in your favourite IDE and they can take advantage of refactoring tools.

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