/****************************************************
* Section : 15
* Machine No. : N
* Roll No. : 18CS100XY
* Name : Soumyajit Dey, Aritra Hazra
* Assignment No : 5c
* Description : Determines All Subsets of {1,2,...,n}
*****************************************************/

#include <stdio.h>
#define MAX 100000

void printSubsets(int a[], int n, int i)
{
    int j,k;

    if (i > 0)
    {
        printf("{ ");
        for (j=0,k=i; j<n; j++,k=k/2)
        { /* checking jth bit is set in i. If it is set,
             then fetch the element at jth index in array */
            if(k%2) /* if(i & (1 << j)) <-- using bitwise opertors */
            {
                printf("%d ", a[j]);
            }
        }
        printf("}\n");
        
        /* recursive call */
        printSubsets(a, n, i-1);
    }
}

int main()
{
    int n, i, noOfSubsets = 1;
    int a[MAX];
    
    /* reads user inputs */
    printf("Enter an Integer (>= 0): ");
    scanf("%d", &n);
    
    /* displays all the subsets */
    if(n<=0)
    {
        printf("NULL Set!\n");
        return;
    }
    
    /* populating elements {1,2,...,n} into array
       and determining number of subsets = 2^n */
    for(i=0; i<n; ++i)
    {
        a[i] = i+1;
        noOfSubsets = noOfSubsets * 2;
    }
    
    printf("The Subsets of { ");
    for(i=0; i<n; ++i)
        printf("%d ", a[i]);
    printf("} are:\n");
    printSubsets(a,n,noOfSubsets);

    return 0;
}