csrabbitspheasants.cs

// Copyright 2010-2021 Google LLC
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

using System;
using Google.OrTools.ConstraintSolver;

/**
 * Shows how to write a custom decision builder.
 */
public class AssignFirstUnboundToMin : NetDecisionBuilder
{
    public AssignFirstUnboundToMin(IntVar[] vars)
    {
        vars_ = vars;
    }

    public override Decision Next(Solver solver)
    {
        foreach (IntVar var in vars_)
        {
            if (!var.Bound())
            {
                return solver.MakeAssignVariableValue(var, var.Min());
            }
        }
        return null;
    }

    private IntVar[] vars_;
}

public class CsRabbitsPheasants
{
    /**
     * Solves the rabbits + pheasants problem.  We are seeing 20 heads
     * and 56 legs. How many rabbits and how many pheasants are we thus
     * seeing?
     */
    private static void Solve()
    {
        Solver solver = new Solver("RabbitsPheasants");
        IntVar rabbits = solver.MakeIntVar(0, 100, "rabbits");
        IntVar pheasants = solver.MakeIntVar(0, 100, "pheasants");
        solver.Add(rabbits + pheasants == 20);
        solver.Add(rabbits * 4 + pheasants * 2 == 56);
        DecisionBuilder db = new AssignFirstUnboundToMin(new IntVar[] { rabbits, pheasants });
        solver.NewSearch(db);
        solver.NextSolution();
        Console.WriteLine("Solved Rabbits + Pheasants in {0} ms, and {1} search tree branches.", solver.WallTime(),
                          solver.Branches());
        Console.WriteLine(rabbits.ToString());
        Console.WriteLine(pheasants.ToString());
        solver.EndSearch();
    }

    public static void Main(String[] args)
    {
        Solve();
    }
}