#! /usr/bin/env python3
#
def perfect_shuffle ( deck ):

#*****************************************************************************80
#
## perfect_shuffle() performs a perfect shuffle on a deck of cards.
#
#  Licensing:
#
#    This code is distributed under the MIT license. 
#
#  Modified:
#
#    16 February 2025
#
#  Author:
#
#    John Burkardt
#
#  Input:
#
#    integer deck[52]: the indices of the cards in a deck.
#
  import numpy as np

  deck_size = len ( deck )
  deck_size_half = deck_size // 2
  deck_shuffled = np.zeros ( deck_size, dtype = int )
  deck_shuffled[0:deck_size:2] = deck[0:deck_size_half]
  deck_shuffled[1:deck_size:2] = deck[deck_size_half:]

  return deck_shuffled

def perfect_shuffle_test ( ):

#*****************************************************************************80
#
## perfect_shuffle_test() tests perfect_shuffle().
#
#  Licensing:
#
#    This code is distributed under the MIT license. 
#
#  Modified:
#
#    16 February 2025
#
#  Author:
#
#    John Burkardt
#
  import numpy as np

  print ( '' )
  print ( 'perfect_shuffle_test():' )
  print ( '  Test perfect_shuffle(), which does a perfect shuffle' )
  print ( '  of a deck of cards.' )

  deck_size = 52
  deck = np.arange ( deck_size, dtype = int )
  print ( '' )
  print ( '  Starting deck:' )
  print ( deck )
#
#  Now do a perfect shuffle.
#
  deck = perfect_shuffle ( deck )
  print ( '' )
  print ( '  Deck after 1 perfect shuffle:' )
  print ( deck )
#
#  Now do 7 more perfect shuffles.
#
  for i in range ( 0, 7 ):
    deck = perfect_shuffle ( deck )
  print ( '' )
  print ( '  Deck after 7 more perfect shuffles:' )
  print ( deck )

  return

if ( __name__ == "__main__" ):
  perfect_shuffle_test ( )