advent_or_day18.mzn

include "globals.mzn";

int: N;
set of int: NODES = 1..N;
int: E;
set of int: EDGES = 1..E;
int: M;
set of int: MANDATORY = 1..M;

array[EDGES] of int: from;
array[EDGES] of int: to;
array[EDGES] of int: weight;
array[MANDATORY] of int: mandatory;

array[NODES] of var bool: node_included;
array[EDGES] of var bool: edge_included;

var min(weight)..sum(weight): total_weight;

constraint forall(m in MANDATORY)(
  node_included[mandatory[m]] = true
);

constraint steiner(N, E, from, to, weight, node_included, edge_included,
                                 total_weight);

solve minimize total_weight;

output [if fix(edge_included[e]) then "\(from[e]) -> \(to[e])\n"  else "" endif | e in EDGES] ++ ["\ntotal_cost: \(_objective)"];

% Solution (Chuffed)
7 -> 29
18 -> 28
18 -> 43
20 -> 7
20 -> 27
20 -> 48
21 -> 12
22 -> 20
22 -> 21
22 -> 43
27 -> 34
28 -> 24
29 -> 33
33 -> 35
36 -> 49
41 -> 22
41 -> 36
41 -> 47
47 -> 37

total_cost: 82
% time elapsed: 168msec

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