#! /usr/bin/env python
#
def compnz_enum ( n, k ):

#*****************************************************************************80
#
## COMPNZ_ENUM returns the number of nonzero compositions of the N into K parts.
#
#  Discussion:
#
#    A composition of the integer N into K nonzero parts is an ordered sequence
#    of K positive integers which sum to N.  The compositions (1,2,1)
#    and (1,1,2) are considered to be distinct.
#
#    The 10 compositions of 6 into three nonzero parts are:
#
#      4 1 1,  3 2 1,  3 1 2,  2 3 1,  2 2 2,  2 1 3,
#      1 4 1,  1 3 2,  1 2 3,  1 1 4.
#
#    The formula for the number of compositions of N into K nonzero
#    parts is
#
#      Number = ( N - 1 )! / ( ( N - K )! * ( K - 1 )! )
#
#    (Describe the composition using N-K '1's and K-1 dividing lines '|'.
#    The number of distinct permutations of these symbols is the number
#    of compositions into nonzero parts.  This is equal to the number of
#    permutations of  N-1 things, with N-K identical of one kind
#    and K-1 identical of another.)
#
#    Thus, for the above example, we have:
#
#      Number = ( 6 - 1 )! / ( ( 6 - 3 )! * ( 3 - 1 )! ) = 10
#
#  Licensing:
#
#    This code is distributed under the GNU LGPL license.
#
#  Modified:
#
#    14 December 2014
#
#  Author:
#
#    John Burkardt
#
#  Reference:
#
#    Albert Nijenhuis, Herbert Wilf,
#    Combinatorial Algorithms for Computers and Calculators,
#    Second Edition,
#    Academic Press, 1978,
#    ISBN: 0-12-519260-6,
#    LC: QA164.N54.
#
#  Parameters:
#
#    Input, integer N, the integer whose compositions are desired.
#
#    Input, integer K, the number of parts in the composition.
#
#    Output, integer VALUE, the number of compositions of N into
#    K nonzero parts.
#
  from i4_choose import i4_choose

  value = i4_choose ( n - 1, n - k )

  return value

def compnz_enum_test ( ):

#*****************************************************************************80
#
## COMPNZ_ENUM_TEST tests COMPNZ_ENUM.
#
#  Licensing:
#
#    This code is distributed under the GNU LGPL license. 
#
#  Modified:
#
#    14 December 2014
#
#  Author:
#
#    John Burkardt
#
  import platform

  n_max = 7

  print ( '' )
  print ( 'COMPNZ_ENUM_TEST:' )
  print ( '  Python version: %s' % ( platform.python_version ( ) ) )
  print ( '  COMPNZ_ENUM returns the number of nonzero compositions' )
  print ( '  of N into K parts.' )
  print ( '' )
  print ( '   N\K ', end = '' )
  for k in range ( 0, n_max + 1 ):
    print ( '  %4d' % ( k ), end = '' )
  print ( '' )
  print ( '' )
  for n in range ( 0, n_max + 1 ):
    print ( '  %2d:  ' % ( n ), end = '' )
    for k in range ( 0, n + 1 ):
      value = compnz_enum ( n, k )
      print ( '  %4d' % ( value ), end = '' )
    print ( '' )
#
#  Terminate.
#
  print ( '' )
  print ( 'COMPNZ_ENUM_TEST:' )
  print ( '  Normal end of execution.' )
  return

if ( __name__ == '__main__' ):
  from timestamp import timestamp
  timestamp ( )
  compnz_enum_test ( )
  timestamp ( )