This program converts an array of format {a1,a2,...an,b1,b2,...bn} to {a1,b1,a2,b2,...an,bn}

ArrangeAlternate.java

/**
 * Created with IntelliJ IDEA.
 * User: Ravi
 * Date: 10/15/13
 * Time: 7:51 PM
 * To change this template use File | Settings | File Templates.
 */
public class ArrangeAlternate {
    public static void main( String[] args )
    {
        int[] array = {1,3,5,7,2,4,6,8};
        interleave(array);
        for( int i = 0; i < array.length; i++ )
        {
            System.out.print( array[i] + " ");
        }
    }
    public static void interleave(int[] array)
    {
        int i = 0;
        int j = 0;
        int mid = (array.length/2) - 1;//points the end of first half

        //the outer loop runs for (length/2) - 1 times
        for( i = 0; i < mid ; i++ )
        {
            //runs for (i+1) times
            for( j = 0; j <= i; j++ )
            {
                //calculate the indices to be swapped
                int l = mid - i + (2 * j);
                int r = mid - i + (2 * j) + 1;

                //swap the elements at left (l) and right (r)
                int temp = array[l];
                array[l] = array[r];
                array[r] = temp;
            }
        }

    }
}