/* 

  Global constraint derangement in Picat.

  From Global Constraint Catalogue
  http://www.emn.fr/x-info/sdemasse/gccat/Cderangement.html
  """
  Enforce to have a permutation with no cycle of length one. The permutation 
  is depicted by the succ attribute of the NODES collection.
  
  Example
      (
     <
     index-1    succ-2,
     index-2    succ-1,
     index-3    succ-5,
     index-4    succ-3,
     index-5    succ-4
     >
     )
  In the permutation of the example we have the following 2 cycles: 1->2->1 and
  3->5->4->3. Since these cycles have both a length strictly greater than 
  one the corresponding derangement constraint holds.
  """

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

*/

import cp.


main => go.

go ?=>
  N = 5,

  X = new_list(N),
  X :: 1..N,

  % X = [2,1,5,3,4],
  derangement(X),

  solve(X),
  println(X),
  fail,
  nl.

go => true.


derangement(X) =>
  subcircuit(X),
  foreach(I in 1..X.len)
     X[I] #!= I
  end.