/*

  Hamming distance in Picat.
 
  I.e. the number of bits differing in two (binary) arrays.
  See http://en.wikipedia.org/wiki/Hamming_distance

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

*/

import cp.

main => go.

% 
% We can now either
% - Calculate the hamming distance from two arrays
% - Given the distance, generate all arrays which has the 
%   Hamming distance.
% 

go ?=>

   N = 6, % length of the arrays
   A = new_list(N),
   A :: 0..1,
   B = new_list(N), 
   B :: 0..1,

   Diffs :: 0..N, % The number of differences 
   % Diffs #= 2,
   indomain(Diffs),


   A = [1,1,1,1,1,1],

   hamming_distance(A,B,Diffs),

   Vars = A ++ B ++ [Diffs],
   solve(Vars),

   writeln(diffs=Diffs),
   writeln(a=A),
   writeln(b=B),nl,
   fail.

go => true.

hamming_distance(As, Bs, Diffs) =>
   Diffs #= sum([(A #!= B) : {A,B} in zip(As,Bs)]).