Reverser.java

/*
 * (C) Copyright 2001 Arnaud Bailly (arnaud.oqube@gmail.com),
 *     Yves Roos (yroos@lifl.fr) and others.
 *
 * 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 rationals.transformations;


import rationals.Automaton;
import rationals.Builder;
import rationals.NoSuchStateException;
import rationals.State;
import rationals.Transition;

import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;

/**
 * Computes the reversal of an Automaton.
 * <p /> 
 * <ul>
 * <li>C = A-</li>
 * <li>S(C) = S(A)</li>
 * <li>S0(C) = T(A)</li>
 * <li>T(C) = S0(A)</li>
 * <li>D(C) = { (s1,a,s2) | exists (s2,a,s1) in D(A)  }</li>
 * </ul>
 *
 * @version $Id: Reverser.java 2 2006-08-24 14:41:48Z oqube $
 */
public class Reverser<L, Tr extends Transition<L>, T extends Builder<L, Tr, T>> implements UnaryTransformation<L, Tr, T> {

  public Automaton<L, Tr, T> transform(Automaton<L, Tr, T> a) {
    Automaton<L, Tr, T> b = new Automaton<>() ;
    Map<State, State> map = new HashMap<>() ;
    Iterator<State> i1 = a.states().iterator() ;
    while(i1.hasNext()) {
      State e = i1.next() ;
      map.put(e , b.addState(e.isTerminal() , e.isInitial())) ;
    }
    Iterator<Transition<L>> i2 = a.delta().iterator() ;
    while(i2.hasNext()) {
      Transition<L> t = i2.next() ;
      try {
        b.addTransition(new Transition<L>(map.get(t.end()), t.label(), map.get(t.start())));
      } catch(NoSuchStateException x) {}
    }
    return b;
  }
}