Java数组中如何高效生成所有两位以上元素的组合和排列？

import java.util.*;

public class Test {

    public static void combine(int[] nums, int start, int k, List<Integer> current, List<List<Integer>> result) {
        if (k == 0) {
            result.add(new ArrayList<>(current));
            return;
        }
        for (int i = start; i < nums.length - k + 1; i++) {
            current.add(nums[i]);
            combine(nums, i + 1, k - 1, current, result);
            current.remove(current.size() - 1);
        }
    }

    public static void permutation(List<Integer> nums, int start, List<List<Integer>> result) {
        if (start == nums.size()) {
            result.add(new ArrayList<>(nums));
            return;
        }
        for (int i = start; i < nums.size(); i++) {
            Collections.swap(nums, start, i);
            permutation(nums, start + 1, result);
            Collections.swap(nums, start, i); // backtrack
        }
    }

    public static void main(String[] args) {
        int[] nums = {11, 33, 22};
        List<List<Integer>> combinations = new ArrayList<>();
        for (int i = 2; i <= nums.length; i++) {
            combine(nums, 0, i, new ArrayList<>(), combinations);
        }

        List<List<Integer>> allPermutations = new ArrayList<>();
        for (List<Integer> combination : combinations) {
            permutation(combination, 0, allPermutations);
        }

        System.out.println(allPermutations);
    }
}