# include <cstdlib>
# include <iostream>
bool open ( int n, int d[] );

using namespace std;

int main ( )
//
//  LOCK_COUNTING uses the COUNTING algorithm to determine the combination of a lock.
//
{
  int d[4], dmin = 0, dmax = 9, i, inc, n = 4;
  bool found;
//
//  Initialize.
//
  for ( i = 0; i < n; i++ )
  {
    d[i] = dmin;
  }

  found = false;

  while ( true )
  {
//
//  Is this the correct combination?
//
    if ( open ( n, d ) )
    {
      found = true;
      cout << "\n";
      cout << "  Found the combination:  ";
      for ( i = 0; i < n; i++ )
      {
        cout << " " << d[i];
      }
      cout << "\n";
      break;
    }
//
//  Try the next combination.
//
    inc = -1;
    for ( i = n - 1; 0 <= i; i-- )
    {
      if ( d[i] == dmax )
      {
        d[i] = dmin;
      }
      else
      {
        inc = i;
        d[i] = d[i] + 1;
        break;
      }
    }
//
//  If INC is still -1, we didn't find anything to increment, and we are done!
//
    if ( inc == -1 )
    {
      break;
    }
  }

  if ( !found )
  {
    cout << "\n";
    cout << "We did not find the combination!\n";
  }

  return 0;
}
bool open ( int n, int d[] )
{
  bool value;

  if ( d[0] == 2 &&
       d[1] == 0 &&
       d[2] == 1 &&
       d[3] == 1 )
  {
    value = true;
  }
  else
  {
    value = false;
  }
  return value;
}