Java數組中如何高效生成所有兩位以上元素的組合和排列？

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);     } }