Thread: Trying to write Factoring Numbers Code--Please Help.

I am trying to finish the code for a simple program that will break a number down and give you the factors of that number. I have the program working all for one part. Right now it returns something like "2*2*2*5*5*" and instead I want it to say 2^3+5^2. Can anyone tell me what I would need to have to do this? I need to use some type of loop I think, and a While statement maybe?

import java.util.*;
 
class Factor
{
    String factor(int n)
    {
        String S = "";
        int f = 2;
        while (n > 1)
            if (n%f == 0)
            {
                S += f + "*";
                n /= f;
            }
            else
                f++;
            return S;
    }
 
    public void setN(int n)
    {
        n = 0;
    }
 
    public void getN(int n)
    {
 
    }
 
}
 
class FactorDemo // main Class
        {
            public static void main(String [] args)
            {
                Scanner in = new Scanner(System.in);
 
                Factor ML = new Factor();
 
                System.out.print("Enter a positive integer(-1 to stop):");
                int n = in.nextInt();
 
                while (n > 0) //0 or negative number to stop the program
                              // is called a sentinel
                {
                    System.out.println(ML.factor(n));
 
                    System.out.print("Enter a positive integer(-1 to stop):");
                    n = in.nextInt();
                }
 
                System.out.println("Thanks for using my program.");
 
            }
        }

You want to make some sort of int array in your factor method. Then use that int array to determine how many instances of x number appears. I would advise a List (such as a Vector) since you will not need to worry about size. Here is what you need:

String factor(int n)
{
	String s;
	//Create Integer Vector
	Vector<Integer> numbers = new Vector<Integer>();
  	int f = 2;
  	while (n > 1)
	{
		if (n%f == 0)
		{
			//Add number to Integer Vector
			numbers.add(new Integer(f));
			n /= f;
		}
		else
			f++;
	}
	//Go through Vector. Doing this way because we will remove from the list as we go
	while(numbers.size()>0)
	{
		//Get number and remove it to allow counting
		Integer tempNumber = numbers.remove(i);
		//Counter Variable
		int numberOfTimes = 1;
		//I think this works, not entirely sure
		while(numbers.indexOf(tempNumber)!=-1)
		{
			//Remove this number from the Vector
			numbers.remove(numbers.indexOf(tempNumber));
			//Increment counter
			numberOfTimes++;
		}
		if(numberOfTimes==1)
			s+=tempNumber+"*";
		else
			s+=tempNumber+"^"+numberOfTimes+"*";
	}
	//Remove the last * symbol
	return (S.substring(0,s.length()-1));
}

There is probably a better way, but that is the best I could come up with without putting more effort in. I haven't tested the code, so tell me if it doesnt work.