Determining if a string is a Palindrome using recursion

Below is an example of how to determine if a word is a palindrome using recursion. A Palindrome is a string that could be read the same way in either direction such as racecar, mom, and even a. This tutorial expects you to understands the following.

C++ Recursion

Example of finding if a word is a palindrome

To determine if a word is a palindrome do the following.

1. Compare the first and last character
2. If these characters are the same, disregard these characters and repeat until one one character or no characters remain

Example:

// Check first and last character
[ r ] [ a ] [ c ] [ e ] [ c ] [ a ] [ r ]

// Second iteration
[ a ] [ c ] [ e ] [ c ] [ a ]

// Third iteration
[ c ] [ e ] [ c ]  

// Fourth iteration
[ e ]

// The word is a palindrome.
 

Now let’s try one that isn’t a palindrome.

// First iteration
[ t ] [ a ] [ b ] [ t ]

// In our second iteration, a and b don’t match
[ a ] [ b ]

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Reversing the elements of a vector using recursion

Below is an example of how to reverse the elements of a vector using recursion. This tutorial expects you to understand the following.

C++ Recursion

Example of reversing the elements of a vector

Below is an example of how one would reverse the elements of a vector by simply intuition.

// Our vector with size 5
[ X ] [ B ] [ A ] [ N ] [ Y ]
[ 0 ] [ 1 ] [ 2 ] [ 3 ] [ 4 ]

//Step 1: Swap entry 0 (first) with the entry n (last)
[ Y ] [ B ] [ A ] [ N ] [ X ]
[ 0 ] [ 1 ] [ 2 ] [ 3 ] [ 4 ]

//Step 2: Swap entry 1 with entry 3 (n -1)
[ Y ] [ N ] [ A ] [ B ] [ X ]
[ 0 ] [ 1 ] [ 2 ] [ 3 ] [ 4 ]

//Step 3: No swap needed for 3rd entry (or middle entry)
[ Y ] [ N ] [ A ] [ B ] [ X ]
[ 0 ] [ 1 ] [ 2 ] [ 3 ] [ 4 ]
 

Notice how once we arrive at the entry in the middle of the vector we don’t continue. Why? The values beyond this entry have already been swapped. Keep this in mind.

Reversing the elements of a vector using iteration

Before we try making a recursive function to reverse the elements of a vector, let’s make one using iteration. By following the method described in the method above, it’s easy to see that we are simply swapping the ith and (nth – ith) variables (Example: the 0th and the 4th (4th – 0th) element).

Reversing the elements of a vector using iteration

The iterative solution for reversing the elements of a vector is below. Make sure you are trying all these functions if you haven’t before on your own.

//We pass the vector by reference
void reverseElements(vector <int> &vec) {

     //Temp variable for swapping
     int temp;

     int n = vec.size()-1;
 
     //Iterate vec.size()/2 times
     for ( int i = 0; i < vec.size()/2; i++ ) {
 
          // The swapping of elements
          temp = vec[i];
          vec[i] = vec[n-i];
          vec[n] = temp;
   
     }

     return;
}

Make sure you understand this completely before moving forward. Try working it out by hand.

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Greatest Common Divisor using the Euclidean Algorithm

• Introduction to Recursion in C++

Euclid’s Algorithm

When studying computer science a famous algorithm taught to students is the Euclidean Algorithm which is used to compute the greatest common divisor of two integers. It’s definition is below.

Computing various examples

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Learn Network Programming

But why learn network programming? At the time of this writing, I’ve been taking a course in Networks and we’ve already programmed quite a simple terminal based instant messaging client in C. You can join and login to a network, create buddies, and have conversations with them. If I was given more time, I would’ve implemented a gui but since we were given a one week period to work on it I didn’t have as much freedom as I had hoped for. I did use the following guide to understand network programming and I don’t think I could have found a faster and easier way to learn than this.

Beej’s Guide to Network Programming

Lighthouse, a short movie

The Fibonacci Sequence

• Introduction to Recursion in C++

Fibonacci is a well known number sequence that models the growth of a rabbit population amongst other things found in nature.

Below is the Fibonacci numbers computed up to the 11th term.

Iterative version of Fibonacci

Fibonacci Formula

Fibonacci(0) = 0;
Fibonacci(1) = 1;
Fibonacci(n) = Fibonacci(n-1) + Fibonacci(n-2);

So how would we do an iterative version? I’ll walk you through the code.

So how would we compute the value of the nth value of the Fibonacci sequence? We can do it with a for loop, to add UP to the value we are looking for. In other words, if we were doing it by hand, we’d do it as following:
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How to install Ubuntu using VirtualBox

Today, we are going to teach you how to use VirtualBox to install Ubuntu using Windows. (This could easily be done on Linux, or a Mac too.) This is a great option for those of you who want to get a programming environment and those who want to avoid dual-booting your computer since it involves a great risk if done wrong. Virtualizing an OS is an easy task and it only takes a few steps. It should take a new user about five minutes to get going. So let’s get started.

What you need to virtualize Ubuntu on VirtualBox

Step 1: Create a new Virtual Machine