在java中查找给定集合的所有子集，并按此顺序

Question

实际上我想这样写一个给定集合的所有子集:

例如，如果我的集合是A：{1,2}，我希望有{} , {1}，{2}，{1,2}

这就是我尝试的：

    static void printSubsets(java.util.Set<Integer> a) {
            int n = a.size();
            // Run a loop for printing all 2^n
            // subset one by one
            for (int i = 0; i < (1 << n); i++) {
                System.out.print("{");
                // Print current subset
                for (int j = 0; j < n; j++) {
    
                    // (1<<j) is a number with jth bit 1
                    // so when we 'and' them with the
                    // subset number we get which numbers
                    // are present in the subset and which
                    // are not
                    if ((i & (1 << j)) > 0)
                        System.out.print(a.toArray()[j] + ",");
                    if (j == n - 1)
                       System.out.print(a.toArray()[j]);
                }
                System.out.print("} , ");
            }
        }

这是输出{}、{1，}、{2，}、｛1，2，}，我的问题是，。我不希望在每个子集的末尾和整个输出的末尾都有、。你能帮我解决这个问题，让我的输出像＜code＞｛｝、｛1｝、｝2｝、{1,2｝＜/code＞？最后，我想把它们分类

Answer 1

如果允许您使用番石榴，您可以利用它的< code>Sets类和< code>Sets.combinations(Set

static void printSubsets(Set<Integer> a) {

    String combinations = IntStream.rangeClosed(0, a.size()).boxed()
            .flatMap(i -> Sets.combinations(a, i).stream()
                                    .sorted(Comparator.comparingInt(Collections::max)))
            .map(subSet -> subSet.stream().sorted().map(String::valueOf)
                                    .collect(Collectors.joining(",", "{", "}")))
            .collect(Collectors.joining(" , "));

    System.out.println(combinations);
}

然后：

Set<Integer> set = Set.of(1, 2);

printSubsets(set);

输出：

{} , {1} , {2} , {1,2}