조합(=combination) 구하기

조합(combination) 구하기

  public static void main(String[] args) {
      String[] testArgs = {"001", "002", "003", "004"};

      List<List<String>> powerSet = new LinkedList<>();

      for (int i = 1; i <= testArgs.length; i++) {
          powerSet.addAll(combination(Arrays.asList(testArgs), i));
      }

      System.out.println(powerSet);
  }

  public static <T> List<List<T>> combination(List<T> values, int size) {
      if (0 == size) {
          return Collections.singletonList(Collections.emptyList());
      }

      if (values.isEmpty()) {
          return Collections.emptyList();
      }

      List<List<T>> combination = new LinkedList<>();

      T actual = values.iterator().next();

      List<T> subSet = new LinkedList<T>(values);
      subSet.remove(actual);

      List<List<T>> subSetCombination = combination(subSet, size - 1);

      for (List<T> set : subSetCombination) {
          List<T> newSet = new LinkedList<T>(set);
          newSet.add(0, actual);
          combination.add(newSet);
      }

      combination.addAll(combination(subSet, size));

      return combination;
  }

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