covering_opl.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 System.Collections;
using System.IO;
using System.Text.RegularExpressions;
using Google.OrTools.ConstraintSolver;

public class SetCoveringOPL
{

  /**
   *
   * Solves a set covering problem.
   * See  See http://www.hakank.org/or-tools/set_covering_opl.py
   *
   */
  private static void Solve()
  {

    Solver solver = new Solver("SetCoveringOPL");

    //
    // data
    //
    int num_workers = 32;
    int num_tasks = 15;

    // Which worker is qualified for each task.
    // Note: This is 1-based and will be made 0-base below.
    int[][] qualified =   {
      new int[] { 1,  9, 19,  22,  25,  28,  31 },
      new int[] { 2, 12, 15, 19, 21, 23, 27, 29, 30, 31, 32 },
      new int[] { 3, 10, 19, 24, 26, 30, 32 },
      new int[] { 4, 21, 25, 28, 32 },
      new int[] { 5, 11, 16, 22, 23, 27, 31 },
      new int[] { 6, 20, 24, 26, 30, 32 },
      new int[] { 7, 12, 17, 25, 30, 31 } ,
      new int[] { 8, 17, 20, 22, 23  },
      new int[] { 9, 13, 14,  26, 29, 30, 31 },
      new int[] { 10, 21, 25, 31, 32 },
      new int[] { 14, 15, 18, 23, 24, 27, 30, 32 },
      new int[] { 18, 19, 22, 24, 26, 29, 31 },
      new int[] { 11, 20, 25, 28, 30, 32 },
      new int[] { 16, 19, 23, 31 },
      new int[] { 9, 18, 26, 28, 31, 32 }
    };

    int[] cost = {1, 1, 1, 1, 1, 1, 1, 1, 2, 2, 2, 2, 2, 2, 2, 3,
                  3, 3, 3, 4, 4, 4, 4, 5, 5, 5, 6, 6, 6, 7, 8, 9};


    //
    // Decision variables
    //
    IntVar[] hire = solver.MakeIntVarArray(num_workers, 0, 1, "workers");
    IntVar total_cost = hire.ScalProd(cost).Var();

    //
    // Constraints
    //

    for(int j = 0; j < num_tasks; j++) {
      // Sum the cost for hiring the qualified workers
      // (also, make 0-base).
      int len = qualified[j].Length;
      IntVar[] tmp = new IntVar[len];
      for(int c = 0; c < len; c++) {
        tmp[c] = hire[qualified[j][c] - 1];
      }
      solver.Add(tmp.Sum() >= 1);
    }


    //
    // objective
    //
    OptimizeVar objective = total_cost.Minimize(1);


    //
    // Search
    //
    DecisionBuilder db = solver.MakePhase(hire,
                                          Solver.CHOOSE_FIRST_UNBOUND,
                                          Solver.ASSIGN_MIN_VALUE);

    solver.NewSearch(db, objective);

    while (solver.NextSolution()) {
      Console.WriteLine("Cost: " + total_cost.Value());
      Console.Write("Hire: ");
      for(int i = 0; i < num_workers; i++) {
        if (hire[i].Value() == 1) {
          Console.Write(i + " ");
        }
      }
      Console.WriteLine("\n");

    }

    Console.WriteLine("\nSolutions: {0}", solver.Solutions());
    Console.WriteLine("WallTime: {0}ms", solver.WallTime());
    Console.WriteLine("Failures: {0}", solver.Failures());
    Console.WriteLine("Branches: {0} ", solver.Branches());

    solver.EndSearch();

  }

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