Decider
An Open Source .Net Constraint Programming Solver
Installation
Install using nuget for .Net Standard 2.1
dotnet add package Decider
Variables
Create constrained integer variables
var s = new VariableInteger("s", 0, 9);
var e = new VariableInteger("e", 0, 9);
var n = new VariableInteger("n", 0, 9);
var d = new VariableInteger("d", 0, 9);
var m = new VariableInteger("m", 1, 9);
var o = new VariableInteger("o", 0, 9);
var r = new VariableInteger("r", 0, 9);
var y = new VariableInteger("y", 0, 9);
var c0 = new VariableInteger("c0", 0, 1);
var c1 = new VariableInteger("c1", 0, 1);
var c2 = new VariableInteger("c2", 0, 1);
var c3 = new VariableInteger("c3", 0, 1);Constraints
Define the constraints of your problem
var constraints = new List<IConstraint>
{
new AllDifferentInteger(new [] { s, e, n, d, m, o, r, y }),
new ConstraintInteger(d + e == (10 * c0) + y),
new ConstraintInteger(n + r + c0 == (10 * c1) + e),
new ConstraintInteger(e + o + c1 == (10 * c2) + n),
new ConstraintInteger(s + m + c2 == (10 * c3) + o),
new ConstraintInteger(c3 == m)
};Search
Find a solution using Decider's search routines
var variables = new [] { c0, c1, c2, c3, s, e, n, d, m, o, r, y };
var state = new StateInteger(variables, constraints);
var searchResult = state.Search();
Console.WriteLine($" {s} {e} {n} {d} ");
Console.WriteLine($" + {m} {o} {r} {e} ");
Console.WriteLine(" ---------");
Console.WriteLine($" {m} {o} {n} {e} {y} ");
Console.WriteLine($"Runtime:\t{state.Runtime}\nBacktracks:\t{state.Backtracks}\n");Which results in
9 5 6 7
+ 1 0 8 5
---------
1 0 6 5 2
Runtime: 00:00:00.0290211
Backtracks: 85
Find All Solutions
Display all solutions to the n-queens problem
var searchResult = state.SearchAllSolutions();
foreach (var solution in state.Solutions)
{
for (var i = 0; i < variables.Length; ++i)
{
for (var j = 0; j < variables.Length; ++j)
Console.Write(solution[i.ToString()].InstantiatedValue == j ? "Q " : ". ");
Console.WriteLine();
}
Console.WriteLine();
}Which results in
Q . . . . . . .
. . . . Q . . .
. . . . . . . Q
. . . . . Q . .
. . Q . . . . .
. . . . . . Q .
. Q . . . . . .
. . . Q . . . .
Q . . . . . . .
. . . . . Q . .
. . . . . . . Q
. . Q . . . . .
. . . . . . Q .
. . . Q . . . .
. Q . . . . . .
. . . . Q . . .
and a further ninety solutions.
Optimise
Create an integer variable to optimise i.e. make as large as possible
var optimise = new VariableInteger("optimalAnswer", 0, 1000);
new ConstraintInteger(optimise == a + b + c + d + e + f + g + h)Specify an upper time bound on how long you search, say, five minutes
var timeout = 60 * 5;
var searchResult = state.Search(optimise, timeout);
Console.WriteLine($"Optimal answer found is ${state.OptimalSolution["optimalAnswer"]}");Constrained Arrays
Index integer arrays with constrained integer variables
var a = new VariableInteger("a", 0, 9);
var array = new ConstrainedArray(new int[] { 0, 23, 52, 62, 75, 73, 47, 20, 87, 27 });
var constraint = new ConstraintInteger(array[a] < 40)F#
Thanks to contributor @toburger, there's a simple example of using Decider in F#.
let constraints: IConstraint list = [
ConstraintInteger(kickboards + cityrollers == expr rollers)
ConstraintInteger(kickboards * expr 3 + cityrollers * expr 2 == expr rolls)
]See Examples/FSharp for full details.
More Examples?
Fork the repo to see more examples, some toy and some real world, of Decider in action.
Licence
Released under the MIT licence, Decider is freely available for commercial use.
Author
I have a PhD in Constraint Programming and love turning NP-complete problems into CSPs. Visit my blog at http://lifebeyondfife.com/.