RabbitsPheasants.java

// Copyright 2010-2021 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.
package com.google.ortools.java;

import com.google.ortools.Loader;
import com.google.ortools.constraintsolver.ConstraintSolverParameters;
import com.google.ortools.constraintsolver.DecisionBuilder;
import com.google.ortools.constraintsolver.IntVar;
import com.google.ortools.constraintsolver.Solver;
import java.util.logging.Logger;

/** Sample showing how to model using the constraint programming solver.*/
public class RabbitsPheasants {
  private static Logger logger = Logger.getLogger(RabbitsPheasants.class.getName());

  /**
   * Solves the rabbits + pheasants problem.  We are seing 20 heads
   * and 56 legs. How many rabbits and how many pheasants are we thus
   * seeing?
   */
  private static void solve(boolean traceSearch) {
    ConstraintSolverParameters parameters = ConstraintSolverParameters.newBuilder()
                                                .mergeFrom(Solver.defaultSolverParameters())
                                                .setTraceSearch(traceSearch)
                                                .build();
    Solver solver = new Solver("RabbitsPheasants", parameters);
    IntVar rabbits = solver.makeIntVar(0, 100, "rabbits");
    IntVar pheasants = solver.makeIntVar(0, 100, "pheasants");
    solver.addConstraint(solver.makeEquality(solver.makeSum(rabbits, pheasants), 20));
    solver.addConstraint(solver.makeEquality(
        solver.makeSum(solver.makeProd(rabbits, 4), solver.makeProd(pheasants, 2)), 56));
    DecisionBuilder db =
        solver.makePhase(rabbits, pheasants, Solver.CHOOSE_FIRST_UNBOUND, Solver.ASSIGN_MIN_VALUE);
    solver.newSearch(db);
    solver.nextSolution();
    logger.info(rabbits.toString());
    logger.info(pheasants.toString());
    solver.endSearch();
  }

  public static void main(String[] args) throws Exception {
    Loader.loadNativeLibraries();
    boolean traceSearch = args.length > 0 && args[1].equals("--trace");
    RabbitsPheasants.solve(traceSearch);
  }
}