/*

  Trains in Picat.

  This is a simple example using table constraint. 
  From SWI prolog manual
  http://www.swi-prolog.org/pldoc/doc_for?object=section%282%2c%20%27A.7%27%2c%20swi%28%27%2fdoc%2fManual%2fclpfd.html%27%29%29
  """
  As another example, consider a train schedule represented as a list
  of quadruples, denoting departure and arrival places and times for each 
  train. In the following program, Ps is a feasible journey of length 
  3 from A to D via trains that are part of the given schedule.
  """

  Answer:
  [[1,2,0,1],[2,3,4,5],[3,4,8,9]]


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

*/

import cp.

main => go.

go =>
   threepath(1, 4, Ps,TotalTime),
   println(Ps),
   println(total_time=TotalTime),nl.

% Valid tuples for the table constraint
trains(Allowed) => 
  Allowed = [{1,2,0,1},{2,3,4,5},{2,3,0,1},{3,4,5,6},{3,4,2,3},{3,4,8,9}].
 
threepath(A, D, Ps,TotalTime) =>

   Ps = [{A,B,_T0,T1},{B,C,T2,T3},{C,D,T4,_T5}],
   T2 #> T1,
   T4 #> T3,
   trains(Ts),
   % Table constraint
   table_in(Ps,Ts),

   TotalTime #= sum([ End-Start :  (_,_,Start,End) in Ps]).