C++ Program to Generate All Possible Subsets with Exactly k Elements in Each Subset

This is a C++ program to generate all possible subsets with exactly k elements in each subset.

Algorithms

Begin
   function PossibleSubSet(char a[], int reqLen, int s, int currLen, bool check[], int l):
   If currLen > reqLen
   Return
   Else if currLen = reqLen
      Then print the new generated sequence.
   If s = l
      Then return no further element is left.
      For every index there are two options:
         either proceed with a start as ‘true’ and recursively call PossibleSubSet()
         with incremented value of ‘currLen’ and ‘s’.
         Or proceed with a start as ‘false’ and recursively call PossibleSubSet()
         with only incremented value of ‘s’.
End

Example

#include<iostream>
using namespace std;
void PossibleSubSet(char a[], int reqLen, int s, int currLen, bool check[], int l)
//print the all possible combination of given array set
{
   if(currLen > reqLen)
   return;
   else if (currLen == reqLen) {
      cout<<"\t";
      for (int i = 0; i < l; i++) {
         if (check[i] == true) {
            cout<<a[i]<<" ";
         }
      }
      cout<<"\n";
      return;
   }
   if (s == l) {
      return;
   }
   check[s] = true;
   PossibleSubSet(a, reqLen, s + 1, currLen + 1, check, l);
   //recursively call PossibleSubSet() with incremented value of ‘currLen’ and ‘s’.
   check[s] = false;
   PossibleSubSet(a, reqLen, s + 1, currLen, check, l);
   //recursively call PossibleSubSet() with only incremented value of ‘s’.
}
int main() {
   int i,n,m;
   bool check[n];
   cout<<"Enter the number of elements: ";
   cin>>n;
   char a[n];
   cout<<"\n";
   for(i = 0; i < n; i++) {
      cout<<"Enter "<<i+1<<" element: ";
      cin>>a[i];
      check[i] = false;
   }
   cout<<"\nEnter the length of the subsets required: ";
   cin>>m;
   cout<<"\nThe possible combination of length "<<m<<" for the given array set:\n";
   PossibleSubSet(a, m, 0, 0, check, n);
   return 0;
}

Output

Enter the number of elements: 7
Enter 1 element: 7
Enter 2 element: 6
Enter 3 element: 5
Enter 4 element: 4
Enter 5 element: 3
Enter 6 element: 2
Enter 7 element: 1
Enter the length of the subsets required: 6
The possible combination of length 6 for the given array set:
7 6 5 4 3 2
7 6 5 4 3 1
7 6 5 4 2 1
7 6 5 3 2 1
7 6 4 3 2 1
7 5 4 3 2 1
6 5 4 3 2 1