/*

  A dinner problem in SWI Prolog

  http://www.sellsbrothers.com/spout/#The_Logic_of_Logic
  """
  My son came to me the other day and said, "Dad, I need help with a"
  "math problem." The problem went like this:

    * We're going out to dinner taking 1-6 grandparents, 1-10 parents and/or 1-40 children
    * Grandparents cost $3 for dinner, parents $2 and children $0.50
    * There must be 20 total people at dinner and it must cost $20
    * How many grandparents, parents and children are going to dinner?
  """

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

*/

:- use_module(library(clpfd)).
:- use_module(hakank_utils).

go :-

   findall([grandparents=Grandparents, 
                parents=Parents, 
                children=Children], 
          dinner([Grandparents,
                  Parents,
                  Children]),L),
   writeln(L),
   nl.

dinner([Grandparents, Parents, Children]) :-
   Grandparents in 0..100,
   Parents      in 0..100,
   Children     in 0..100,
   Grandparents * 3 + Parents * 2 + Children // 2 #= 20,

   Grandparents + Parents + Children #= 20, % number of people = 20

   % must be some of each
   Grandparents #> 0,
   Parents      #> 0,
   Children     #> 0,
   
   label([Grandparents, Parents, Children]).