129 lines
3.9 KiB
Java
129 lines
3.9 KiB
Java
// Copyright 2011 Hakan Kjellerstrand hakank@gmail.com
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package com.google.ortools.contrib;
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import com.google.ortools.Loader;
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import com.google.ortools.constraintsolver.DecisionBuilder;
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import com.google.ortools.constraintsolver.IntVar;
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import com.google.ortools.constraintsolver.OptimizeVar;
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import com.google.ortools.constraintsolver.Solver;
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import java.io.*;
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import java.text.*;
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import java.util.*;
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public class SetCoveringDeployment {
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/**
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* Solves a set covering deployment problem. See
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* http://www.hakank.org/google_or_tools/set_covering_deployment.py
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*/
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private static void solve() {
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Solver solver = new Solver("SetCoveringDeployment");
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//
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// data
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//
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// From http://mathworld.wolfram.com/SetCoveringDeployment.html
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String[] countries = {
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"Alexandria", "Asia Minor", "Britain", "Byzantium", "Gaul", "Iberia", "Rome", "Tunis"};
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int n = countries.length;
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// the incidence matrix (neighbours)
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int[][] mat = {{0, 1, 0, 1, 0, 0, 1, 1}, {1, 0, 0, 1, 0, 0, 0, 0}, {0, 0, 0, 0, 1, 1, 0, 0},
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{1, 1, 0, 0, 0, 0, 1, 0}, {0, 0, 1, 0, 0, 1, 1, 0}, {0, 0, 1, 0, 1, 0, 1, 1},
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{1, 0, 0, 1, 1, 1, 0, 1}, {1, 0, 0, 0, 0, 1, 1, 0}};
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//
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// variables
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//
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// First army
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IntVar[] x = solver.makeIntVarArray(n, 0, 1, "x");
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// Second (reserve) army
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IntVar[] y = solver.makeIntVarArray(n, 0, 1, "y");
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// total number of armies
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IntVar num_armies = solver.makeSum(solver.makeSum(x), solver.makeSum(y)).var();
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//
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// constraints
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//
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//
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// Constraint 1: There is always an army in a city
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// (+ maybe a backup)
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// Or rather: Is there a backup, there
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// must be an an army
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//
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for (int i = 0; i < n; i++) {
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solver.addConstraint(solver.makeGreaterOrEqual(x[i], y[i]));
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}
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//
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// Constraint 2: There should always be an backup
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// army near every city
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//
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for (int i = 0; i < n; i++) {
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ArrayList<IntVar> count_neighbours = new ArrayList<IntVar>();
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for (int j = 0; j < n; j++) {
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if (mat[i][j] == 1) {
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count_neighbours.add(y[j]);
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}
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}
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solver.addConstraint(solver.makeGreaterOrEqual(
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solver.makeSum(x[i], solver.makeSum(count_neighbours.toArray(new IntVar[1])).var()), 1));
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}
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//
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// objective
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//
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OptimizeVar objective = solver.makeMinimize(num_armies, 1);
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//
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// search
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//
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DecisionBuilder db = solver.makePhase(x, solver.INT_VAR_DEFAULT, solver.INT_VALUE_DEFAULT);
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solver.newSearch(db, objective);
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//
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// output
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//
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while (solver.nextSolution()) {
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System.out.println("num_armies: " + num_armies.value());
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for (int i = 0; i < n; i++) {
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if (x[i].value() == 1) {
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System.out.print("Army: " + countries[i] + " ");
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}
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if (y[i].value() == 1) {
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System.out.println("Reserve army: " + countries[i]);
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}
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}
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}
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solver.endSearch();
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// Statistics
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System.out.println();
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System.out.println("Solutions: " + solver.solutions());
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System.out.println("Failures: " + solver.failures());
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System.out.println("Branches: " + solver.branches());
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System.out.println("Wall time: " + solver.wallTime() + "ms");
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}
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public static void main(String[] args) throws Exception {
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Loader.loadNativeLibraries();
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SetCoveringDeployment.solve();
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}
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}
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