Java 计算一组数的所有子集

你想要的就是Powerset。这是一个简单的实现：

public static Set<Set<Integer>> powerSet(Set<Integer> originalSet) {        Set<Set<Integer>> sets = new HashSet<Set<Integer>>();        if (originalSet.isEmpty()) { sets.add(new HashSet<Integer>()); return sets;        }        List<Integer> list = new ArrayList<Integer>(originalSet);        Integer head = list.get(0);        Set<Integer> rest = new HashSet<Integer>(list.subList(1, list.size()));        for (Set<Integer> set : powerSet(rest)) { Set<Integer> newSet = new HashSet<Integer>(); newSet.add(head); newSet.addAll(set); sets.add(newSet); sets.add(set);        }        return sets;    }

我将为你提供一个示例，说明该算法如何用于的幂集{1, 2, 3}：

• Remove

  {1}

  , and execute powerset for

  {2, 3}

  ;
• Remove

  {2}

  , and execute powerset for

  {3}

  ;
  • Remove

    {3}

    , and execute powerset for

    {}

    ;
  • Powerset of

    {}

    is

    {{}}

    ;
  • Powerset of

    {3}

    is

    3

    combined with

    {{}} = { {}, {3} }

    ;
• Powerset of

  {2, 3} is {2}

  combined with

  { {}, {3} } = { {}, {3}, {2}, {2, 3} }

  ;
• Powerset of

  {1, 2, 3} is {1}

  combined with

  { {}, {3}, {2}, {2, 3} } = { {}, {3}, {2}, {2, 3}, {1}, {3, 1}, {2, 1}, {2, 3, 1} }.