Return the cross product of a list of lists

Question

Given a list of size n, Write a program that returns all possible combination of elements contained in each list.

Example:

• List A = \"x, z\"

Answer 1

As you know, the usual solution is recursion. However, out of boredom I once wrote a java method multiNext to do this without recursion. multiNext uses an array to keep track of a load of indices in an equivalent system of nested loops.

public static boolean multiNext(int[] current, int[] slotLengths) {
    for (int r = current.length - 1; r >= 0; r--) {
        if (current[r] < slotLengths[r] - 1) {
            current[r]++;
            return true;
        } else {
            current[r] = 0;
        }
    }
    return false;
}

public static void cross(List> lists) {
    int size = lists.size();
    int[] current = new int[size];
    int[] slotLengths = new int[size];
    for (int i = 0; i < size; i++)
        slotLengths[i] = lists.get(i).size();
    do {
        List temp = new ArrayList<>();
        for (int i = 0; i < size; i++)
            temp.add(lists.get(i).get(current[i]));
        System.out.println(temp);
    } while (multiNext(current, slotLengths));
}

public static void main(String[] args) {
    cross(Arrays.asList(Arrays.asList("x", "z"), Arrays.asList("a", "b", "c"), Arrays.asList("o", "p")));
}