// Finding fermion basis states
// using stl algorithm next_permutation
#include <iostream>
#include <vector>
#include <algorithm>
#include <iterator>
#include <map>

using namespace std;

void vector_out(vector<int> v)
{
  copy(v.begin(),v.end(), // from
       ostream_iterator<int>(cout," ")); // to 
  cout<<endl;
}

int main () {
  const int N=6; // single-fermion states
  const int Nfermions=3; // number of fermions

  cout<<"All "<<Nfermions<<"-fermion states for N="<<N<<endl;
  vector<int> state;
  for (int i=0;i<N;++i) {
    if(i<Nfermions) {
      state.push_back(1);
    }
    else {
      state.push_back(0);
    }	
  }
  sort (state.begin(),state.end()); 
  int i = 1;
  vector<int> fermistate(N);
  do {
    cout<<"state # "<<i<<" is  ";
    vector_out(state);
    ++i;
  } while (next_permutation (state.begin(),state.end()));
  cout<<"found "<<i-1<<" fermion states\n";
  return 0;
}