Algorithms in Java

Written By : Debasis Das (25-Jan-2015)

Program to generate Excel Column Headers in Java

In a Mac Excel there are 16384 Columns per sheet with the starting column of index 0 being A and the last column header is XFD with index 16383 (N-1)
In this program we will generate the column header alphabets using a simple Java Program.

import java.util.ArrayList;
import java.util.Arrays;
public class ExcelHeader {

	public static void main(String[] args) {
		String [] alphabets = new String[]{"A","B","C","D","E","F","G","H","I","J","K","L","M","N","O","P","Q","R","S","T","U","V","W","X","Y","Z"};
		
		ArrayList <String> newAlphabetArray = new ArrayList();
		int endIndex = 16384; //The maximum number of columns available in Excel sheet
		for (int i=0; i<endIndex; i++)
		{
	        int quotient = i/26;
	        int remainder = i%26;
	        int secondLevelQuotient;
	        int secondLevelRemainder;
	        
	        String alpha;
	        if (quotient == 0)
	        {
	        	alpha = alphabets[remainder];
	        	newAlphabetArray.add(alpha);
	        }
	        else if (quotient > 0 && quotient < 27)
	        {
	        	alpha = alphabets[quotient-1] + alphabets[remainder]; 
	        	newAlphabetArray.add(alpha);	            
	        	
	        }
	        else if (quotient >26)
	        {
	            secondLevelQuotient = quotient / 26;
	            secondLevelRemainder = quotient % 26;
	            if (secondLevelRemainder == 0)
	            {
	            	alpha = alphabets[secondLevelQuotient-1]+alphabets[secondLevelRemainder]+alphabets[remainder];
	            }
	            else
	            {
	            	alpha = alphabets[secondLevelQuotient-1]+alphabets[secondLevelRemainder-1]+alphabets[remainder];
	            }
	            newAlphabetArray.add(alpha);
	        }
		}
		System.out.println(newAlphabetArray.get(16383)); //Should print XFD
	}
}

Bubble Sort Algorithm in Java

import java.util.Arrays;
public class BubbleSort {

    public static void main(String[] args) {
        int[] myIntArray = new int[]{120,200,301,543,234,19,87,67,54,37,89};
        System.out.println(Arrays.toString(myIntArray));
        
        //Begin Bubble Sort Algorithm
        boolean dataExchanged = true;
        int length = myIntArray.length - 1;
        while ((length > 0) && (dataExchanged))
        {
            dataExchanged = false;
            for (int i = 0; i< length; i++)
            {
                if (myIntArray[i] > myIntArray[i+1])
                {
                    //Do Swap
                    int temp = myIntArray[i];
                    myIntArray[i] = myIntArray[i+1];
                    myIntArray[i+1] = temp;
                    dataExchanged = true;
                    
                }
            }
            length = length - 1;
        }
        //End Bubble Sort Algorithm
        System.out.println(Arrays.toString(myIntArray));
    }
}

Selection Sort Algorithm in Java

import java.util.Arrays;
public class SelectionSort {
public static void main(String[] args) {
    int[] myIntArray = new int[]{120,200,301,543,234,19,87,67,54,37,89};
    System.out.println("Before Sorting " + Arrays.toString(myIntArray));
    //Begin Selection Sort Algorithm
    int i,j;
    int indexOfMin;
    int length = myIntArray.length;
    for (j=0; j < length - 1; j++)
    {
        //Assume that the first element is the minimum
        indexOfMin = j;
        //Test against elements after j to find a new smallest.
        for (i = j+1; i< length; i++)
        {
            if (myIntArray[i] < myIntArray[indexOfMin])
            {
                //It means we have found a new minimum. We need to remember its index.
                indexOfMin = i;
            }
        }
        if (indexOfMin !=j)
        {
            //Do a swap
            int temp = myIntArray[j];
            myIntArray[j] = myIntArray[indexOfMin];
            myIntArray[indexOfMin] = temp;
        }
    }
    //End Selection Sort Algorithm
    System.out.println("After Selection Sorting " + Arrays.toString(myIntArray));
}
}