How to create cartesian product over arbitrary groups of numbers in Java?

Question

Let\'s say I have 2 groups of numbers:

{1, 2, 3},
{4, 5}

I\'d like to create an algorithm (in Java) that outputs the following 6 combinations:<

Answer 1

Got a bit bored and decided to give it a shot. Should be exactly what you need:

public static void main(String args[]) {

    ArrayList input = new ArrayList();
    input.add(new int[] { 1, 2, 3 });
    input.add(new int[] { 4, 5 });
    input.add(new int[] { 6, 7 });

    combine(input, new int[input.size()], 0);
}

private static void combine(ArrayList input, int[] current, int k) {

    if(k == input.size()) {
        for(int i = 0; i < k; i++) {
            System.out.print(current[i] + " ");
        }
        System.out.println();
    } else {            
        for(int j = 0; j < input.get(k).length; j++) {
            current[k] = input.get(k)[j];
            combine(input, current, k + 1);
        }       
    }
}