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MiniZinc

/***
!Test
expected:
- !Result
solution: !Solution
Num: [1, 25, 2, 16, 3, 22, 4, 13, 19, 5, 17, 26, 6, 14, 23, 10, 20, 18, 7, 15, 11, 27, 8, 24, 21, 12, 9]
Pos: [1, 3, 5, 7, 10, 13, 19, 23, 27, 16, 21, 26, 8, 14, 20, 4, 11, 18, 9, 17, 25, 6, 15, 24, 2, 12, 22]
- !Result
solution: !Solution
Num: [19, 13, 7, 22, 16, 25, 8, 14, 20, 10, 9, 17, 23, 15, 11, 26, 21, 4, 18, 12, 5, 24, 1, 6, 2, 27, 3]
Pos: [23, 25, 27, 18, 21, 24, 3, 7, 11, 10, 15, 20, 2, 8, 14, 5, 12, 19, 1, 9, 17, 4, 13, 22, 6, 16, 26]
- !Result
solution: !Solution
Num: [1, 25, 2, 4, 3, 22, 5, 10, 16, 6, 19, 26, 11, 13, 23, 17, 7, 12, 20, 14, 8, 27, 18, 24, 9, 15, 21]
Pos: [1, 3, 5, 4, 7, 10, 17, 21, 25, 8, 13, 18, 14, 20, 26, 9, 16, 23, 11, 19, 27, 6, 15, 24, 2, 12, 22]
- !Result
solution: !Solution
Num: [1, 22, 2, 25, 3, 13, 4, 16, 19, 5, 23, 14, 6, 26, 17, 10, 20, 15, 7, 24, 11, 18, 8, 27, 21, 12, 9]
Pos: [1, 3, 5, 7, 10, 13, 19, 23, 27, 16, 21, 26, 6, 12, 18, 8, 15, 22, 9, 17, 25, 2, 11, 20, 4, 14, 24]
- !Result
solution: !Solution
Num: [7, 10, 19, 22, 8, 25, 11, 13, 9, 16, 20, 12, 23, 14, 4, 26, 17, 5, 21, 15, 6, 24, 1, 18, 2, 27, 3]
Pos: [23, 25, 27, 15, 18, 21, 1, 5, 9, 2, 7, 12, 8, 14, 20, 10, 17, 24, 3, 11, 19, 4, 13, 22, 6, 16, 26]
- !Result
solution: !Solution
Num: [7, 10, 19, 25, 8, 16, 11, 22, 9, 13, 20, 12, 17, 26, 4, 14, 23, 5, 21, 18, 6, 15, 1, 27, 2, 24, 3]
Pos: [23, 25, 27, 15, 18, 21, 1, 5, 9, 2, 7, 12, 10, 16, 22, 6, 13, 20, 3, 11, 19, 8, 17, 26, 4, 14, 24]
***/
%-----------------------------------------------------------------------------%
% Langford's Problem (CSPlib problem 24)
%
% June 2006; Sebastian Brand
%
% Instance L(k,n):
% Arrange k sets of numbers 1 to n so that each appearance of the number m is m
% numbers on from the last. For example, the L(3,9) problem is to arrange 3
% sets of the numbers 1 to 9 so that the first two 1's and the second two 1's
% appear one number apart, the first two 2's and the second two 2's appear two
% numbers apart, etc.
%-----------------------------------------------------------------------------%
% MiniZinc version
% Peter Stuckey September 30
include "globals.mzn";
%-----------------------------------------------------------------------------%
% Instance
%-----------------------------------------------------------------------------%
% int: n = 10; % numbers 1..n
% int: k = 2; % sets 1..k
int: n = 9;
int: k = 3;
%-----------------------------------------------------------------------------%
% Input
%-----------------------------------------------------------------------------%
set of int: numbers = 1..n; % numbers
set of int: sets = 1..k; % sets of numbers
set of int: num_set = 1..n*k;
set of int: positions = 1..n*k; % positions of (number, set) pairs
%-----------------------------------------------------------------------------%
% Primal model
%-----------------------------------------------------------------------------%
array[num_set] of var positions: Pos;
% Pos[ns]: position of (number, set)
% pair in the sought sequence
constraint
forall(i in 1..n, j in 1..k-1) (
Pos[k*(i-1) + j+1] - Pos[k*(i-1) + j] = i+1
);
constraint
alldifferent(Pos);
%-----------------------------------------------------------------------------%
% Dual model (partial)
%-----------------------------------------------------------------------------%
array[positions] of var num_set: Num; % Num[p]: (number, set) pair at
% position p in the sought sequence
constraint
alldifferent(Num);
%-----------------------------------------------------------------------------%
% Channelling between primal model and dual model
%-----------------------------------------------------------------------------%
constraint
forall(i in numbers, j in sets, p in positions) (
(Pos[k*(i-1) + j] = p) <-> (Num[p] = k*(i-1) + j)
);
%-----------------------------------------------------------------------------%
% Without specifying a sensible search order this problem takes
% forever to solve.
%
solve :: int_search(Pos, first_fail, indomain_split, complete)
satisfy;
output
[ if j = 1 then "\n" ++ show(i) ++ "s at " else ", " endif ++
show(Pos[k*(i-1) + j])
| i in 1..n, j in 1..k
] ++
[ "\n" ];