mr_smith.cs

//
// Copyright 2012 Hakan Kjellerstrand
//
// 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;

public class MrSmith
{
  /**
   *
   * Mr Smith problem.
   *
   * From an IF Prolog example (http://www.ifcomputer.de/)
   * """
   * The Smith family and their three children want to pay a visit but they
   * do not all have the time to do so. Following are few hints who will go
   * and who will not:
   *  o If Mr Smith comes, his wife will come too.
   *  o At least one of their two sons Matt and John will come.
   *  o Either Mrs Smith or Tim will come, but not both.
   *  o Either Tim and John will come, or neither will come.
   *  o If Matt comes, then John and his father will
   *    also come.
   * """
   * 
   * The answer should be:
   * Mr_Smith_comes      =  0
   * Mrs_Smith_comes     =  0
   * Matt_comes          =  0
   * John_comes          =  1
   * Tim_comes           =  1
   *
   *
   * Also see http://www.hakank.org/or-tools/mr_smith.py
   *
   */
  private static void Solve()
  {
    Solver solver = new Solver("MrSmith");

    //
    // Data
    //
    int n = 5;

    //
    // Decision variables
    //
    IntVar[] x = solver.MakeIntVarArray(n, 0, 1, "x");
    IntVar Mr_Smith  = x[0];
    IntVar Mrs_Smith = x[1];
    IntVar Matt      = x[2];
    IntVar John      = x[3];
    IntVar Tim       = x[4];


    //
    // Constraints
    //

    //
    // I've kept the MiniZinc constraints for clarity
    // and debugging.
    //

    // If Mr Smith comes then his wife will come too.
    // (Mr_Smith -> Mrs_Smith)
    solver.Add(Mr_Smith - Mrs_Smith <= 0);

    // At least one of their two sons Matt and John will come.
    // (Matt \/ John)
    solver.Add(Matt+John >= 1);

    // Either Mrs Smith or Tim will come but not both.
    // bool2int(Mrs_Smith) + bool2int(Tim) = 1
    // (Mrs_Smith xor Tim)
    solver.Add(Mrs_Smith + Tim == 1);

    // Either Tim and John will come or neither will come.
    // (Tim = John)
    solver.Add(Tim == John);

    // If Matt comes /\ then John and his father will also come.
    // (Matt -> (John /\ Mr_Smith))
    solver.Add(Matt - (John*Mr_Smith) <= 0);



    //
    // Search
    //
    DecisionBuilder db = solver.MakePhase(x,
                                          Solver.CHOOSE_MIN_SIZE_LOWEST_MIN,
                                          Solver.ASSIGN_CENTER_VALUE);

    solver.NewSearch(db);

    while (solver.NextSolution()) {
      for(int i = 0; i < n; i++) {
        Console.Write(x[i].Value() + " ");
      }
      Console.WriteLine("\n");
      Console.WriteLine("Mr Smith : {0}", Mr_Smith.Value());
      Console.WriteLine("Mrs Smith: {0}", Mrs_Smith.Value());
      Console.WriteLine("Matt     : {0}", Matt.Value());
      Console.WriteLine("John     : {0}", John.Value());
      Console.WriteLine("Tim      : {0}", Tim.Value());

    }

    Console.WriteLine("\nSolutions: " + solver.Solutions());
    Console.WriteLine("WallTime: " + solver.WallTime() + "ms ");
    Console.WriteLine("Failures: " + solver.Failures());
    Console.WriteLine("Branches: " + solver.Branches());

    solver.EndSearch();

  }

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