How to make combination function generic

[Anjali Pal]

Hi all,

I have written a function which generates combination in a desired order. The code is somthing like this

   

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;


public class ArrayTest {

	protected Object[] buildArray3(int min, int max,int noOfControls, boolean varyOnMin) {
		List result = new ArrayList();
		Integer[] tempArray=null ;
		result.add(Collections.EMPTY_LIST); // Empty
		int iMax = (varyOnMin ? max : min);

		for (int i = min; i <= iMax; i++) {
			tempArray = new Integer[1];
			tempArray[0]=i;
			result.add(Arrays.asList(tempArray));
			for(int j = i ;j<=max;j++)
			{
				if(i!=j){
					tempArray = new Integer[2];
					tempArray[0]=i;
					tempArray[1]=j;
					result.add(Arrays.asList(tempArray));
					for(int k=j ;k<=max;k++){
						if(j!=k){
							tempArray = new Integer[3];
							tempArray[0]=i;
							tempArray[1]=j;
							tempArray[2]=k;
							result.add(Arrays.asList(tempArray));
						}

					}

				}				

			}

		}
		return result.toArray();
	}

	public static void main(String[] args) {
		ArrayTest arrayTest = new ArrayTest();
		Object [] obj = arrayTest.buildArray3(1, 5, 3, true);
		int count=0;
		for (Object i : obj){
			
			System.out.println("count = "+count +"      " +i);
			count++;
		}	

	}
}


 

The output of this code is and this is what is required :

    
count = 0      []
count = 1      [1]
count = 2      [1, 2]
count = 3      [1, 2, 3]
count = 4      [1, 2, 4]
count = 5      [1, 2, 5]
count = 6      [1, 3]
count = 7      [1, 3, 4]
count = 8      [1, 3, 5]
count = 9      [1, 4]
count = 10      [1, 4, 5]
count = 11      [1, 5]
count = 12      [2]
count = 13      [2, 3]
count = 14      [2, 3, 4]
count = 15      [2, 3, 5]
count = 16      [2, 4]
count = 17      [2, 4, 5]
count = 18      [2, 5]
count = 19      [3]
count = 20      [3, 4]
count = 21      [3, 4, 5]
count = 22      [3, 5]
count = 23      [4]
count = 24      [4, 5]
count = 25      [5]

My problem is all the hard coding in that function i am passing "min" "max" for range of digits and this part is ok (more or less)
Please ignore the Boolean value.

"noOfControls" is something i need to implement ie all the combination i am getting are 3 digits max (governed by number of for loop).

I need to remove this dependency i don't want to write new method every time say "if i need series upto 6 digits and write method with 6 loops"

My question is what should be the approach ?
and what are the possible ways to do it.

Thanks in advance.

[Rob Spoor]

Check out recursion. You create a private method that takes the number of elements to add. When initially called with 6, you take one element, then call the same method but with 5 this time. Continue until the count is 1.