Metaheuristiques/src/main/java/jobshop/solvers/RandomSolver.java

package jobshop.solvers;

import jobshop.*;
import jobshop.encodings.JobNumbers;
import jobshop.encodings.Schedule;

import java.awt.*;
import java.util.ArrayList;
import java.util.Optional;
import java.util.Random;

/** A solver that generates random solutions until a deadline is met.
 *  Then returns the best solution that was generated.
 */
public class RandomSolver implements Solver {

    int pts = 10;

    @Override
    public ArrayList<Result> solve(Instance instance, long deadline) {
        Random generator = new Random(0);

        JobNumbers sol = new JobNumbers(instance);

        // initialize a first solution to the problem.
        for (int j = 0; j < instance.numJobs; j++) {
            for (int t = 0; t < instance.numTasks; t++) {
                sol.addTaskOfJob(j);
            }
        }
        // best solution is currently the initial one
        Optional<Schedule> best = sol.toSchedule();

        // while we have some time left, generate new solutions by shuffling the current one
        while (deadline - System.currentTimeMillis() > 1) {
            shuffleArray(sol.jobs, generator);
            Optional<Schedule> candidate = sol.toSchedule();
            if (candidate.isPresent()) {
                if (best.isEmpty() || candidate.get().makespan() < best.get().makespan()) {
                    best = candidate;
                }
            }
        }

        Result result = new Result(instance, best, Result.ExitCause.Timeout);
        ArrayList<Result> list = new ArrayList<>();
        int i;
        for (i=0; i<pts; i++) {
            list.add(result);
        }
        return list;
    }

    /**
     * Simple Fisher–Yates array shuffling
     */
    private static void shuffleArray(int[] array, Random randomNumberGenerator) {
        int index;
        for (int i = array.length - 1; i > 0; i--) {
            index = randomNumberGenerator.nextInt(i + 1);
            if (index != i) {
                array[index] ^= array[i];
                array[i] ^= array[index];
                array[index] ^= array[i];
            }
        }
    }

    @Override
    public void setIterMax(int iterMax) {
    }

    @Override
    public void setpts(int pts) {this.pts = pts;}

}