furniture_moving_intervals.cs

// Copyright 2010-2022 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 System.Collections;
using System.Linq;
using Google.OrTools.ConstraintSolver;

public class FurnitureMovingIntervals
{
    /**
     *
     * Moving furnitures (scheduling) problem in Google CP Solver.
     *
     * Marriott & Stukey: 'Programming with constraints', page  112f
     *
     * Also see http://www.hakank.org/or-tools/furniture_moving.py
     *
     */
    private static void Solve()
    {
        Solver solver = new Solver("FurnitureMovingIntervals");

        const int n = 4;
        int[] durations = { 30, 10, 15, 15 };
        int[] demand = { 3, 1, 3, 2 };
        const int upper_limit = 160;
        const int max_num_workers = 5;

        //
        // Decision variables
        //
        IntervalVar[] tasks = new IntervalVar[n];
        for (int i = 0; i < n; ++i)
        {
            tasks[i] =
                solver.MakeFixedDurationIntervalVar(0, upper_limit - durations[i], durations[i], false, "task_" + i);
        }

        // Fillers that span the whole resource and limit the available
        // number of workers.
        IntervalVar[] fillers = new IntervalVar[max_num_workers];
        for (int i = 0; i < max_num_workers; ++i)
        {
            fillers[i] = solver.MakeFixedDurationIntervalVar(0, 0, upper_limit, true, "filler_" + i);
        }

        // Number of needed resources, to be minimized or constrained.
        IntVar num_workers = solver.MakeIntVar(0, max_num_workers, "num_workers");
        // Links fillers and num_workers.
        for (int i = 0; i < max_num_workers; ++i)
        {
            solver.Add((num_workers > i) + fillers[i].PerformedExpr() == 1);
        }

        // Creates makespan.
        IntVar[] ends = new IntVar[n];
        for (int i = 0; i < n; ++i)
        {
            ends[i] = tasks[i].EndExpr().Var();
        }
        IntVar end_time = ends.Max().VarWithName("end_time");

        //
        // Constraints
        //
        IntervalVar[] all_tasks = new IntervalVar[n + max_num_workers];
        int[] all_demands = new int[n + max_num_workers];
        for (int i = 0; i < n; ++i)
        {
            all_tasks[i] = tasks[i];
            all_demands[i] = demand[i];
        }
        for (int i = 0; i < max_num_workers; ++i)
        {
            all_tasks[i + n] = fillers[i];
            all_demands[i + n] = 1;
        }
        solver.Add(all_tasks.Cumulative(all_demands, max_num_workers, "workers"));

        //
        // Some extra constraints to play with
        //

        // all tasks must end within an hour
        // solver.Add(end_time <= 60);

        // All tasks should start at time 0
        // for(int i = 0; i < n; i++) {
        //   solver.Add(tasks[i].StartAt(0));
        // }

        // limitation of the number of people
        // solver.Add(num_workers <= 3);
        solver.Add(num_workers <= 4);

        //
        // Objective
        //

        // OptimizeVar obj = num_workers.Minimize(1);
        OptimizeVar obj = end_time.Minimize(1);

        //
        // Search
        //
        DecisionBuilder db = solver.MakePhase(all_tasks, Solver.INTERVAL_DEFAULT);

        solver.NewSearch(db, obj);

        while (solver.NextSolution())
        {
            Console.WriteLine(num_workers.ToString() + ", " + end_time.ToString());
            for (int i = 0; i < n; i++)
            {
                Console.WriteLine("{0} (demand:{1})", tasks[i].ToString(), demand[i]);
            }
            Console.WriteLine();
        }

        Console.WriteLine("Solutions: {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();
    }
}