#! /usr/bin/env python3
#
def collatz_path ( n ):

#*****************************************************************************80
#
## collatz_path() uses recursion to print the path of a Collatz sequence.
#
#  Licensing:
#
#    This code is distributed under the MIT license.
#
#  Modified:
#
#    30 June 2017
#
#  Author:
#
#    John Burkardt
#
#  Input:
#
#    integer N, the current member of the path.
#  
  print ( '  %d' % ( n ) )

  if ( n < 1 ):

    print ( '' )
    print ( 'collatz_path - Fatal error!' )
    print ( '  Path member N = %d is not positive.' % ( n ) )
    raise Exception ( 'collatz_path - Fatal error!' )

  elif ( n == 1 ):
    pass
  elif ( ( n % 2 ) == 0 ):
    collatz_path ( int ( n / 2 ) )
  else:
    collatz_path ( 3 * n + 1 )

  return

def collatz_path_test ( ):

#*****************************************************************************80
#
## collatz_path_test() tests collatz_path().
#
#  Licensing:
#
#    This code is distributed under the MIT license.
#
#  Modified:
#
#    30 June 2017
#
#  Author:
#
#    John Burkardt
#
  print ( '' )
  print ( 'collatz_path_test():' )
  print ( '  collatz_path prints the members of a Collatz path.' )

  for n in [ 7, 8, 9, 10, 600 ]:
    print ( '' )
    print ( '  %d is the starting point.' % ( n ) )
    collatz_path ( n )

  return

def collatz_recursive_test ( ):

#*****************************************************************************80
#
## collatz_recursive_test() tests collatz_recursive().
#
#  Licensing:
#
#    This code is distributed under the MIT license.
#
#  Modified:
#
#    30 June 2017
#
#  Author:
#
#    John Burkardt
#
  import platform
  
  print ( '' )
  print ( 'collatz_recursive_test():' )
  print ( '  Python version: %s' % ( platform.python_version ( ) ) )
  print ( '  Test collatz_recursive().' )

  collatz_path_test ( )
#
#  Terminate.
#
  print ( '' )
  print ( 'collatz_recursive_test():' )
  print ( '  Normal end of execution.' )

  return

def timestamp ( ):

#*****************************************************************************80
#
## timestamp() prints the date as a timestamp.
#
#  Licensing:
#
#    This code is distributed under the MIT license. 
#
#  Modified:
#
#    06 April 2013
#
#  Author:
#
#    John Burkardt
#
  import time

  t = time.time ( )
  print ( time.ctime ( t ) )
  
  return None
  
if ( __name__ == '__main__' ):
  timestamp ( )
  collatz_recursive_test ( )
  timestamp ( )