98 lines
2.9 KiB
Java
98 lines
2.9 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 SetCovering {
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/** Solves a set covering problem. See http://www.hakank.org/google_or_tools/set_covering.py */
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private static void solve() {
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Solver solver = new Solver("SetCovering");
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//
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// data
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//
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// Placing of firestations, from Winston 'Operations Research',
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// page 486.
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int min_distance = 15;
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int num_cities = 6;
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int[][] distance = {{0, 10, 20, 30, 30, 20}, {10, 0, 25, 35, 20, 10}, {20, 25, 0, 15, 30, 20},
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{30, 35, 15, 0, 15, 25}, {30, 20, 30, 15, 0, 14}, {20, 10, 20, 25, 14, 0}};
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//
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// variables
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//
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IntVar[] x = solver.makeIntVarArray(num_cities, 0, 1, "x");
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IntVar z = solver.makeSum(x).var();
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//
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// constraints
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//
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// ensure that all cities are covered
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for (int i = 0; i < num_cities; i++) {
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ArrayList<IntVar> b = new ArrayList<IntVar>();
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for (int j = 0; j < num_cities; j++) {
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if (distance[i][j] <= min_distance) {
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b.add(x[j]);
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}
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}
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solver.addConstraint(solver.makeSumGreaterOrEqual(b.toArray(new IntVar[1]), 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(z, 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("z: " + z.value());
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System.out.print("x: ");
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for (int i = 0; i < num_cities; i++) {
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System.out.print(x[i].value() + " ");
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}
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System.out.println();
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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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SetCovering.solve();
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}
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}
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