/* 

  Balanced 0-1 matrix in Picat.

  See
  http://en.wikipedia.org/wiki/Dynamic_programming
  A type of balanced 0-1 matrix
  """
  Consider the problem of assigning values, either zero or one, to the positions 
  of an n x n matrix, n even, so that each row and each column contains 
  exactly n/2 zeros and n/2 ones.
  """


  This Picat model was created by Hakan Kjellerstrand, hakank@gmail.com
  See also my Picat page: http://www.hakank.org/picat/

*/

import cp,util.

main => go.

go ?=>
  N = 6, % must be even
  M = N div 2,

  X = new_array(N,N),
  X :: 0..1,

  
  if N mod 2 != 0 then
    print("N (%d) must be even!", N),
    halt
  end,

  XT = X.transpose,
  foreach(I in 1..N)
     count(1,X[I],M),
     count(1,XT[I],M)
  end,

  solve(X),
  foreach(Row in X) println(Row) end,
  nl,

  fail,

  nl.

go => true.