IteratorLCSAlgorithm.java

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/*
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 *
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/.
 *
 * This file incorporates work covered by the following license notice:
 *
 *   Licensed to the Apache Software Foundation (ASF) under one or more
 *   contributor license agreements. See the NOTICE file distributed
 *   with this work for additional information regarding copyright
 *   ownership. The ASF licenses this file to you 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 .
 */
 
package org.openoffice.xmerge.merger.diff;
 
import java.util.ArrayList;
import org.openoffice.xmerge.merger.DiffAlgorithm;
import org.openoffice.xmerge.merger.Difference;
import org.openoffice.xmerge.merger.Iterator;
import org.openoffice.xmerge.util.Debug;
 
public class IteratorLCSAlgorithm implements DiffAlgorithm {
 
    public Difference[] computeDiffs(Iterator orgSeq, Iterator modSeq) {
 
        int orgSeqlen = orgSeq.elementCount();
        int modSeqlen = modSeq.elementCount();
 
        // Diff table is used to keep track which element is the same or not
        // in those 2 sequences
        int[][] diffTable = createDiffTable(orgSeq, modSeq);
 
        // debug purpose...
        if (Debug.isFlagSet(Debug.INFO)) {
            printDiffTable(diffTable);
        }
 
        ArrayList<Difference> diffResult = new ArrayList<Difference>();
 
        generateResult(diffTable, orgSeqlen, modSeqlen, diffResult);
 
        // convert the vector to array, it has to do in here as
        // generateResult is called recursively
        Difference[] diffArray = new Difference[diffResult.size()];
        diffResult.toArray(diffArray);
 
        return diffArray;
    }
 
    private void printDiffTable(int[][] diffTable) {
 
        for (int i = 0; i < diffTable.length; i++) {
            StringBuilder sb = new StringBuilder();
            for (int j = 0; j < diffTable[i].length; j++) {
               sb.append(" ").append(diffTable[i][j]).append(" ");
            }
            Debug.log(Debug.INFO, sb.toString());
        }
    }
 
    private int[][] createDiffTable(Iterator orgSeq, Iterator modSeq) {
        int orgSeqlen = orgSeq.elementCount() + 1;
        int modSeqlen = modSeq.elementCount() + 1;
        int[][] diffTable;
 
        // initialize the diffTable
        diffTable = new int[orgSeqlen][];
        for (int i = 0; i < orgSeqlen; i++) {
            diffTable[i] = new int[modSeqlen];
        }
 
        // compute the diff Table using LCS algorithm, refer to the book
        // mentioned at the top of the program
 
        int i, j;
 
        Object orgSeqObject, modSeqObject;
 
        for (orgSeqObject = orgSeq.start(), i = 1;
             orgSeqObject != null;
             orgSeqObject = orgSeq.next(), i++) {
 
            for (modSeqObject = modSeq.start(), j = 1;
                 modSeqObject != null;
                 modSeqObject = modSeq.next(), j++) {
 
                if (orgSeq.equivalent(orgSeqObject, modSeqObject)) {
                    diffTable[i][j] = diffTable[i-1][j-1]+1;
                } else {
                    if (diffTable[i-1][j] >= diffTable[i][j-1]) {
                        diffTable[i][j] = diffTable[i-1][j];
                    } else {
                        diffTable[i][j] = diffTable[i][j-1];
                    }
                }
            }
        }
 
        return diffTable;
    }
 
    private void generateResult(int[][] diffTable,
                                int i, int j, ArrayList<Difference> diffVector) {
 
        // handle the first element
        if (i == 0 && j == 0) {
            return;
 
        } else if (j == 0) {
            for (int cnt = 0; cnt < i; cnt++) {
                Difference diff =
                    new Difference(Difference.DELETE, cnt, j);
                diffVector.add(diff);
            }
            return;
 
        } else if (i == 0) {
            for (int cnt = 0; cnt < j; cnt++) {
                Difference diff =
                    new Difference(Difference.ADD, i, cnt);
                diffVector.add(diff);
            }
            return;
        }
 
        // for the detail of this algorithm, refer to the book mentioned on
        // the top and page 317 and 318.
        if ((diffTable[i-1][j-1] == diffTable[i][j] -1) &&
            (diffTable[i-1][j-1] == diffTable[i-1][j]) &&
            (diffTable[i-1][j-1] == diffTable[i][j-1])) {
 
            // the element of ith and jth in org and mod sequence is the same
            generateResult(diffTable, i-1, j-1, diffVector);
        } else {
            if (diffTable[i-1][j] > diffTable[i][j-1]) {
 
                // recursively call first, then add the result so that
                // the beginning of the diffs will be stored first
                generateResult(diffTable, i-1, j, diffVector);
 
                Difference diff =
                    new Difference(Difference.DELETE, i-1, j);
                diffVector.add(diff);
            } else if (diffTable[i-1][j] < diffTable[i][j-1]) {
 
                // recursively call first, then add the result so that
                // the beginning of the diffs will be stored first
                generateResult(diffTable, i, j-1, diffVector);
 
                Difference diff =
                    new Difference(Difference.ADD, i, j-1);
                diffVector.add(diff);
            } else { // diffTable[i-1][j] == diffTable[i][j-1]
                // recursively call first, then add the result so that
                // the beginning of the diffs will be stored first
                generateResult(diffTable, i-1, j-1, diffVector);
 
                Difference diff =
                    new Difference(Difference.CHANGE, i-1, j-1);
                diffVector.add(diff);
 
            }
        }
    }
}