io.fabric8.zjsonpatch.internal.collections4.ListUtils Maven / Gradle / Ivy

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/**
 * Copyright 2016 flipkart.com zjsonpatch.
 *
 * 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 io.fabric8.zjsonpatch.internal.collections4;

import io.fabric8.zjsonpatch.internal.collections4.sequence.CommandVisitor;
import io.fabric8.zjsonpatch.internal.collections4.sequence.EditScript;
import io.fabric8.zjsonpatch.internal.collections4.sequence.SequencesComparator;

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

public class ListUtils {

  //-----------------------------------------------------------------------

  /**
   * Returns the longest common subsequence (LCS) of two sequences (lists).
   *
   * @param  the element type
   * @param a   the first list
   * @param b   the second list
   * @return the longest common subsequence
   * @throws NullPointerException if either list is {@code null}
   * @since 4.0
   */
  public static  List longestCommonSubsequence(final List a, final List b) {
    return longestCommonSubsequence(a, b, DefaultEquator.defaultEquator());
  }

  /**
   * Returns the longest common subsequence (LCS) of two sequences (lists).
   *
   * @param      the element type
   * @param a       the first list
   * @param b       the second list
   * @param equator the equator used to test object equality
   * @return the longest common subsequence
   * @throws NullPointerException if either list or the equator is {@code null}
   * @since 4.0
   */
  public static  List longestCommonSubsequence(final List a, final List b,
                                                     final Equator equator) {
    if (a == null || b == null) {
      throw new NullPointerException("List must not be null");
    }
    if (equator == null) {
      throw new NullPointerException("Equator must not be null");
    }

    final SequencesComparator comparator = new SequencesComparator(a, b, equator);
    final EditScript script = comparator.getScript();
    final LcsVisitor visitor = new LcsVisitor();
    script.visit(visitor);
    return visitor.getSubSequence();
  }

  /**
   * A helper class used to construct the longest common subsequence.
   */
  private static final class LcsVisitor implements CommandVisitor {
    private ArrayList sequence;

    public LcsVisitor() {
      sequence = new ArrayList();
    }

    public void visitInsertCommand(final E object) {
    }

    public void visitDeleteCommand(final E object) {
    }

    public void visitKeepCommand(final E object) {
      sequence.add(object);
    }

    public List getSubSequence() {
      return sequence;
    }
  }

}