This is my recursive solution which can get the power set of any set using Java Generics. Its main idea is to combine the head of the input array with all the possible solutions of the rest of the array as follows.
import java.util.LinkedHashSet;
import java.util.Set;
public class SetUtil {
private static<T> Set<Set<T>> combine(T head, Set<Set<T>> set) {
Set<Set<T>> all = new LinkedHashSet<>();
for (Set<T> currentSet : set) {
Set<T> outputSet = new LinkedHashSet<>();
outputSet.add(head);
outputSet.addAll(currentSet);
all.add(outputSet);
}
all.addAll(set);
return all;
}
//Assuming that T[] is an array with no repeated elements ...
public static<T> Set<Set<T>> powerSet(T[] input) {
if (input.length == 0) {
Set <Set<T>>emptySet = new LinkedHashSet<>();
emptySet.add(new LinkedHashSet<T>());
return emptySet;
}
T head = input[0];
T[] newInputSet = (T[]) new Object[input.length - 1];
for (int i = 1; i < input.length; ++i) {
newInputSet[i - 1] = input[i];
}
Set<Set<T>> all = combine(head, powerSet(newInputSet));
return all;
}
public static void main(String[] args) {
Set<Set<Integer>> set = SetUtil.powerSet(new Integer[] {1, 2, 3, 4, 5, 6});
System.out.println(set);
}
}
This will output:
[[1, 2, 3, 4, 5, 6], [1, 2, 3, 4, 5], [1, 2, 3, 4, 6], [1, 2, 3, 4], [1, 2, 3, 5, 6], [1, 2, 3, 5], [1, 2, 3, 6], [1, 2, 3], [1, 2, 4, 5, 6], [1, 2, 4, 5], [1, 2, 4, 6], [1, 2, 4], [1, 2, 5, 6], [1, 2, 5], [1, 2, 6], [1, 2], [1, 3, 4, 5, 6], [1, 3, 4, 5], [1, 3, 4, 6], [1, 3, 4], [1, 3, 5, 6], [1, 3, 5], [1, 3, 6], [1, 3], [1, 4, 5, 6], [1, 4, 5], [1, 4, 6], [1, 4], [1, 5, 6], [1, 5], [1, 6], [1], [2, 3, 4, 5, 6], [2, 3, 4, 5], [2, 3, 4, 6], [2, 3, 4], [2, 3, 5, 6], [2, 3, 5], [2, 3, 6], [2, 3], [2, 4, 5, 6], [2, 4, 5], [2, 4, 6], [2, 4], [2, 5, 6], [2, 5], [2, 6], [2], [3, 4, 5, 6], [3, 4, 5], [3, 4, 6], [3, 4], [3, 5, 6], [3, 5], [3, 6], [3], [4, 5, 6], [4, 5], [4, 6], [4], [5, 6], [5], [6], []]