powerset

/*
The powerset of any set S is the set of all subsets of S, 
including the empty set and S itself.

To print all subsets, I used recursion and Stack.
Because there are two cases for each element (included or not),
the total subsets is 2^the number of elements,
we can solve this using recursion and Stack.
*/


import java.util.*;

public class Solution {
	
	public static int count = 0;
	public static int[] a = {1,2,3,4,5};
	public static Stack<Integer> st = new Stack<>();
	
	public static void powerset(int i) {
		if (i==a.length) {
			count++;
			System.out.println(st);
			return;
		}
		else {
			st.push(a[i]); //the case of including this element
			powerset(i+1);
			st.pop(); //the case of not including this element
			powerset(i+1);
		}
	}
    public static void main(String[] args) {  
        powerset(0);
        System.out.println("\n" + "The number of subsets: " + count);
    }   
}


/*****
Output:

[1, 2, 3, 4, 5]
[1, 2, 3, 4]
[1, 2, 3, 5]
[1, 2, 3]
[1, 2, 4, 5]
[1, 2, 4]
[1, 2, 5]
[1, 2]
[1, 3, 4, 5]
[1, 3, 4]
[1, 3, 5]
[1, 3]
[1, 4, 5]
[1, 4]
[1, 5]
[1]
[2, 3, 4, 5]
[2, 3, 4]
[2, 3, 5]
[2, 3]
[2, 4, 5]
[2, 4]
[2, 5]
[2]
[3, 4, 5]
[3, 4]
[3, 5]
[3]
[4, 5]
[4]
[5]
[]

The number of subsets: 32
*****/