用Java查找笛卡尔积

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

public class CartesianProduct {
    public static void main(String[] args) {
        List<List<String>> lists = new ArrayList<>();
        lists.add(Arrays.asList("A", "B", "C"));
        lists.add(Arrays.asList("1", "2", "3"));
        lists.add(Arrays.asList("X", "Y", "Z"));

        List<List<String>> cartesianProduct = getCartesianProduct(lists);
        System.out.println(cartesianProduct);
    }

    public static List<List<String>> getCartesianProduct(List<List<String>> lists) {
        List<List<String>> result = new ArrayList<>();
        if (lists == null || lists.isEmpty()) {
            return result;
        }

        int totalSize = 1;
        for (List<String> list : lists) {
            totalSize *= list.size();
        }

        for (int i = 0; i< totalSize; i++) {
            List<String> combination = new ArrayList<>();
            for (int j = 0; j< lists.size(); j++) {
                int index = (i / getCombinationSize(lists, j)) % lists.get(j).size();
                combination.add(lists.get(j).get(index));
            }
            result.add(combination);
        }

        return result;
    }

    private static int getCombinationSize(List<List<String>> lists, int index) {
        int size = 1;
        for (int i = index + 1; i< lists.size(); i++) {
            size *= lists.get(i).size();
        }
        return size;
    }
}

[
  [A, 1, X],
  [A, 1, Y],
  [A, 1, Z],
  [A, 2, X],
  [A, 2, Y],
  [A, 2, Z],
  [A, 3, X],
  [A, 3, Y],
  [A, 3, Z],
  [B, 1, X],
  [B, 1, Y],
  [B, 1, Z],
  [B, 2, X],
  [B, 2, Y],
  [B, 2, Z],
  [B, 3, X],
  [B, 3, Y],
  [B, 3, Z],
  [C, 1, X],
  [C, 1, Y],
  [C, 1, Z],
  [C, 2, X],
  [C, 2, Y],
  [C, 2, Z],
  [C, 3, X],
  [C, 3, Y],
  [C, 3, Z]
]