com.flaptor.indextank.suggest.Automaton.java Source code

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Here is the source code for com.flaptor.indextank.suggest.Automaton.java

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/*
 * Copyright (c) 2011 LinkedIn, Inc
 * 
 * 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.flaptor.indextank.suggest;

import java.util.Set;
import java.util.Stack;

import com.google.common.collect.Sets;

public class Automaton {
    private final State startState;

    public static interface Transition {
        public char getSymbol();

        public State getState();
    }

    public interface State {
        /**
         * @return transitions sorted by transition symbol
         */
        public Iterable<Transition> getTransitions();

        public State step(char symbol);

        public boolean isAccept();
    }

    public Automaton(State startState) {
        this.startState = startState;
    }

    public State getStartState() {
        return startState;
    }

    @SuppressWarnings("unchecked")
    public static Set<String> intersectPaths(Automaton small, Automaton big) {
        class Element {
            String path;
            State smallState;
            State bigState;

            public Element(String path, State smallState, State bigState) {
                this.path = path;
                this.smallState = smallState;
                this.bigState = bigState;
            }
        }

        Set<String> results = Sets.newHashSet();
        Stack<Element> stack = new Stack<Element>();
        stack.push(new Element("", small.getStartState(), big.getStartState()));

        while (!stack.isEmpty()) {
            Element element = stack.pop();

            Iterable<Transition> transitions = element.smallState.getTransitions();

            for (Transition smallTransition : transitions) {
                char symbol = smallTransition.getSymbol();
                State smallState = smallTransition.getState();
                State bigState = element.bigState.step(symbol);

                if (bigState != null) {
                    String path = element.path + symbol;
                    stack.push(new Element(path, smallState, bigState));

                    if (smallState.isAccept() && bigState.isAccept()) {
                        results.add(path);
                    }
                }

            }
        }

        return results;
    }

}