Powerset implementation. How???

Question

Im a writing a program and one of the things it has to do is to construct a powerset from an interger array.
Powerset is a set of all subsets
for example int [] data = {1,2,3,4};
so the powerset should be a two dim array : {{1},{2},{3},{4}, {1,2},{1,3},{1,4},{2,3},{2,4},{3,4},{1,2,3}, {1,2,4},{1,3,4}, {2,3,4}, {1,2,3,4}}
This one is without the empty set - {}; so the number of elements in the powerset is 2^n - 1
I need a method in this form:
/** Takes an integer array and returns the powerset in two dim array */
public int [][] powerset(int [] data){
//some magic code here
So can anyone help me with this. I've been trying to do it myself for 2 days and now i know im completely stuck. Couldnt find any clues on the internet either
Your help would be very appriciated!

Answer 1

Well, having to use arrays leads to a lot of ugly low-level Java code which just gets in the way of the algorithm. But suppose you could work with sets instead. Here's the basic algorithm:public Set powerset(int n) {
  if (n <= 0) return new Set(empty set); // return a set containing a single, empty, set here
  Set p1 = powerset(n-1);
  Set p2 = powerset(n-1);
  // for each Set x in p2, replace it by x union {n}
  return p1 union p2;
}Try this by hand:
powerset(0) = {{}}, a set whose only element is the empty set.
powerset(1) = {{}} union {{1}} = {{} {1}}
powerset(2) = {{} {1}} union {{2} {1 2}} = {{} {1} {2} {1 2}}
and so on.