在Android Studio中计算组合

public class CombinationCalculator {
    public static void main(String[] args) {
        String[] elements = {"A", "B", "C"};
        int r = 2; // 组合的长度

        List<List<String>> combinations = calculateCombinations(elements, r);
        for (List<String> combination : combinations) {
            System.out.println(combination);
        }
    }

    public static List<List<String>> calculateCombinations(String[] elements, int r) {
        List<List<String>> combinations = new ArrayList<>();
        calculateCombinationsHelper(elements, r, 0, new ArrayList<>(), combinations);
        return combinations;
    }

    private static void calculateCombinationsHelper(String[] elements, int r, int start, List<String> currentCombination, List<List<String>> combinations) {
        if (r == 0) {
            combinations.add(new ArrayList<>(currentCombination));
            return;
        }

        for (int i = start; i <= elements.length - r; i++) {
            currentCombination.add(elements[i]);
            calculateCombinationsHelper(elements, r - 1, i + 1, currentCombination, combinations);
            currentCombination.remove(currentCombination.size() - 1);
        }
    }
}