Question

I’d like an help on this algorithm.

I have a text file like this:

input1
input2
etc...

Every inputX has a subset of elements, like:

input1 -> {input1_1, input1_2, ...}
input2 -> {input2_1, input2_2, input_2_3, ...}
inputX -> {inputX_1, inputX_2, inputX_3, ...}

I have to produce something similar at:

input1_1
input2_1
--------

input1_2
input2_1
--------

input1_1
input2_2
--------

input1_2
input2_2
--------

input1_1
input2_3
--------

input1_2
input2_3
--------

Can you suggest some algorithms to me?
All I can think about it’s a while/for loop, but I don’t know how to properly set it.

Thank you very much,
Pierpaolo

Answer 1

If you know how many lists there are, you can do it with nested loops:

for (int i = 0 ; i != input1.size() ; i++)
    for (int j = 0 ; j != input2.size() ; j++)
        for (int k = 0 ; k != input3.size() ; k++) {
            String[] data = new String[] {
                input1.get(i), input2.get(j), input3.get(k)
            };
            Process(data);
        }

If you do not know how many lists there are, you need a recursive solution:

void processCombinations(int[] pos, int n, ArrayList<ArrayList<String> > inputs, String[] soFar) {
    if (n == pos.length) {
        Process(soFar);
        return;
    }
    ArrayList<String> input = inputs.get(n);
    for (pos[n] = 0 ; pos[n] != input.size() ; pos[n]++) {
        soFar[n] = input.get(pos[n]);
        processCombinations(pos, n+1, input, soFar);
    }
}