#include <bits/stdc++.h>
using namespace std;
#define size 4
 
int arr[size] = {1,2,3,4};
vector< vector<int> > all;
 
void generate_powerset(int *temparr, int level, int start)
{
	int i, j;
	vector<int> sub ;
	for(i=start; i<size; i++)
	{
		temparr[level] = arr[i];
		sub.clear();
		// printf("{ ");
		for (j=0; j<=level; j++)
			sub.push_back(temparr[j]); //printf("%d ",temparr[j]);
		all.push_back(sub);
		//  printf("}\n");
		if( i < size-1)
			generate_powerset(temparr, level+1, i+1);
	}
}
 
int main()
{
	printf("{ }\n"); // Empty Set!
	int temparr[size] = {0};
	generate_powerset(temparr, 0, 0);
	for (auto i: all)
    {
        for(auto j : i)
            cout << j << " ";
        cout << endl;
    }
 
}
 

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