Remember that one “Guess the Number” game? Let’s look at the following scenario by applying the Binary Search algorithm in order for you to understand how Binary Search works.

The Guessing Game

Pick a number from 0 – 100 and depending on your guess, I’ll either say Correct, Higher, or Lower. What would you choose?

0

1

…

49

50

51

…

99

100

Well, 50 of course! Why? Best case you get it correct. Worst case you’ll either get a “Higher” or “Lower”. Now think about the following, if you got “Higher” you eliminated 0-49, or 51-100 if “Lower”, in other words, you eliminate HALF the possibilities.

50

51

…

74

75

76

…

99

100

Well, let’s say it was “Higher”. What would you guess after? 75. Since it’s in between 50 – 100. If you didn’t guess correctly, you’ll be facing the similar scenario as before. You’ll end up eliminating half the possibilities!

Binary Search Algorithm

The following is the recursive implementation.

int binarysearch(vector  vec, int low, int high, int key)
{
    //Not found
    if ( low > high )
    {
          return -1;
    }

    //Finding the middle index between high and low
    int mid = (low + high)/2;

    //Returning the index if key is found
    if ( vec[mid] == key )
    {
          return mid;
    }
    //If middle index value is larger than our key, we search the lower half of the vector
    //else we search the upper half of the vector
    else if ( vec[mid] > key )
    {
          return binarysearch(vec, low, mid-1, key);
    }
    else
    {
          return binarysearch(vec, mid+1, high, key);
    }
}

Example of Binary Search

Let’s say our container held the values 0-100 in its respective index values. Let’s say the value we are looking for is 57.

First iteration

50 < 57, so search through the upper half of our vector.

Second iteration

75 > 57, so search through the lower half of our vector.

Third iteration

63 > 57, so search through the lower half of our vector.

Fourth iteration

57 == 57!

Go ahead and give it a try, it will be a great experience to see what was put into making that simple game. Make a modification, or change it completely… you are free to do what you like with it.

Just as a reminder, Diego’s Pong Game will soon have another release along with source code. So stay tuned so you can take a look at the work that it takes to make a simple pong game. I know I’m waiting for it!

Here is the link to the source:
Piranha Plant, Wario, and Coin Game Source

Here is how to set up your environment
Setting up your environment is relatively easy with the following tutorial.
Codeblocks with SDL support

Enjoy!

For now the velocity of the ball is constant. I plan on changing that on my second release so its possible to beat the computer.

This was created using CodeBlocks and an OpenGL/SDL package from a friend of mine. So, soon once I believe the code is user friendly, I’ll release it so anyone can learn and create your own game! Don’t worry, it isn’t difficult. You use C++ and OpenGL/SDL handle all the graphics for you.

Download and comment on the game here.

Controls: You move up and down with W and S.