Decider

An Open Source .Net Constraint Programming Solver

Installation

Install using nuget for .Net Core 8.0 (.Net Standard 2.0 and 2.1 also supported)

 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");
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/.