generate all subsets of size k from a set

Question

I want to generate all the subsets of size k from a set.

eg:-say I have a set of 6 elements, I have to list all the subsets in which the cardinality of elements is 3

Answer 1

 #include 
 #define FIN "subsets.in"
 #define FOUT "subsets.out"
 #define MAXSIZE 100

 void performSubsets(int n, int k){

 int i, j, s, v[ MAXSIZE ]; 

 freopen(FOUT, "w", stdout);


 memset(v, 0, sizeof( v ));

 do {

    v[ n - 1 ]++;

    for(i = n - 1; i >= 1; i--) {

        if(v[ i ] > 1) {

           v[ i ] -= 2;

           v[ i - 1 ] += 1;  
        }
    }

    s = 0;

    for(j = 0; j < n; j++) s += v[j];

    for(j = 0; j < n; j++) 

        if( v[ j ] && s == k) printf("%d ", (j + 1));

   if(s == k) printf("\n");

 } while(s < n);     

fclose( stdout );      

}

int main() {

    int n, k; 

    freopen(FIN, "r", stdin);

    //read n and size k
    scanf("%d %d", &n, &k);

fclose( stdin );

performSubsets(n,k);

}

This problem can be solved using an algorithm non-recursive.