net.oneandone.sushi.util.Lcs Maven / Gradle / Ivy

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/**
 * Copyright 1&1 Internet AG, https://github.com/1and1/
 *
 * 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 net.oneandone.sushi.util;

import java.util.ArrayList;
import java.util.List;

/** Longest common subsequence. http://en.wikipedia.org/wiki/Diff */

public class Lcs {
    private static final List EMPTY = new ArrayList<>(0);

    public static  List compute(List vert, List hor) {
        List[] previous;
        List[] current;
        
        previous = new List[hor.size() + 1];
        for (int i = 0; i < previous.length; i++) {
            previous[i] = (List) EMPTY;
        }

        for (T value : vert) {
            current = new List[hor.size() + 1];
            current[0] = (List) EMPTY;
            for (int i = 1; i < current.length; i++) {
                if (value.equals(hor.get(i - 1))) {
                    current[i] = append(previous[i - 1], value);
                } else {
                    current[i] = longest(current[i - 1], previous[i]);
                }
            }
            previous = current;
        }
        return previous[previous.length - 1];
    }
    
    private static  List append(List lst, T value) {
        List result;
        
        result = new ArrayList<>(lst.size() + 1);
        result.addAll(lst);
        result.add(value);
        return result;
    }
    
    private static  List longest(List a, List b) {
        return new ArrayList<>(a.size() >= b.size() ? a : b);
    }
}