A Generic Text Comparison Tool Implementation with LCS Approach
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Join For FreeDetecting and showing differences of two texts (especially having
hundreds or thousands of lines) is a common problem. Using pure
java.lang.String class methods may be a solution, but the most important
issue for that kind of operations, "performance" will not be
satisfactory. We want an efficient solution which may have a view as
below:
 |
| Text Difference Tool Example |
The problem contains two parts:
- Detecting differences of two texts: For detecting differences, an efficient dynamic algorithm of LCS (Longest Common Subsequence) used in this solution. This solution has O(text1WordCount * text2WordCount) complexity and coded as "longestCommonSubsequence" method below.
- Visualizing the differences: For visualizing, an HTML tag based approach is used, which marks new words of text2 with green color and old words of text1 with red color. This solution has O(changedWordsCount * (text1WordCount+text2WordCount)) complexity and coded as "markTextDifferences" method below.
Note1: For simplicity, "normalizeText" method is used for removing \n, \t and multiple space characters.
Note2: This class
was created as a Vaadin component. But "longestCommonSubsequence" is
pure generic and "markTextDifferences" method is generic on HTML based
visual components, so they can also be used with different frameworks.
import java.util.ArrayList;
import com.vaadin.ui.CustomComponent;
import com.vaadin.ui.Label;
import com.vaadin.ui.Layout;
import com.vaadin.ui.VerticalLayout;
/**
* Text comparison component which marks differences of two texts with colors.
*
* @author cb
*/
public class TextCompareComponent extends CustomComponent {
private Layout mainLayout = new VerticalLayout();
private ArrayList<String> longestCommonSubsequenceList;
private static final String INSERT_COLOR = "#99FFCC";
private static final String DELETE_COLOR = "#CB6D6D";
public TextCompareComponent(String text1, String text2) {
text1 = normalizeText(text1);
text2 = normalizeText(text2);
this.longestCommonSubsequenceList = longestCommonSubsequence(text1, text2);
String result = markTextDifferences(text1, text2,
longestCommonSubsequenceList, INSERT_COLOR, DELETE_COLOR);
Label label = new Label(result, Label.CONTENT_XHTML);
mainLayout.addComponent(label);
setCompositionRoot(mainLayout);
}
/**
* Finds a list of longest common subsequences (lcs) of given two texts.
*
* @param text1
* @param text2
* @return - longest common subsequence list
*/
private ArrayList<String> longestCommonSubsequence(String text1, String text2) {
String[] text1Words = text1.split(" ");
String[] text2Words = text2.split(" ");
int text1WordCount = text1Words.length;
int text2WordCount = text2Words.length;
int[][] solutionMatrix = new int[text1WordCount + 1][text2WordCount + 1];
for (int i = text1WordCount - 1; i >= 0; i--) {
for (int j = text2WordCount - 1; j >= 0; j--) {
if (text1Words[i].equals(text2Words[j])) {
solutionMatrix[i][j] = solutionMatrix[i + 1][j + 1] + 1;
}
else {
solutionMatrix[i][j] = Math.max(solutionMatrix[i + 1][j],
solutionMatrix[i][j + 1]);
}
}
}
int i = 0, j = 0;
ArrayList<String> lcsResultList = new ArrayList<String>();
while (i < text1WordCount && j < text2WordCount) {
if (text1Words[i].equals(text2Words[j])) {
lcsResultList.add(text2Words[j]);
i++;
j++;
}
else if (solutionMatrix[i + 1][j] >= solutionMatrix[i][j + 1]) {
i++;
}
else {
j++;
}
}
return lcsResultList;
}
/**
* Normalizes given string by deleting \n, \t and extra spaces.
*
* @param text - initial string
* @return - normalized string
*/
private String normalizeText(String text) {
text = text.trim();
text = text.replace("\n", " ");
text = text.replace("\t", " ");
while (text.contains(" ")) {
text = text.replace(" ", " ");
}
return text;
}
/**
* Returns colored inserted/deleted text representation of given two texts.
* Uses longestCommonSubsequenceList to determine colored sections.
*
* @param text1
* @param text2
* @param lcsList
* @param insertColor
* @param deleteColor
* @return - colored result text
*/
private String markTextDifferences(String text1, String text2,
ArrayList<String> lcsList, String insertColor, String deleteColor) {
StringBuffer stringBuffer = new StringBuffer();
if (text1 != null && lcsList != null) {
String[] text1Words = text1.split(" ");
String[] text2Words = text2.split(" ");
int i = 0, j = 0, word1LastIndex = 0, word2LastIndex = 0;
for (int k = 0; k < lcsList.size(); k++) {
for (i = word1LastIndex, j = word2LastIndex;
i < text1Words.length && j < text2Words.length;) {
if (text1Words[i].equals(lcsList.get(k)) &&
text2Words[j].equals(lcsList.get(k))) {
stringBuffer.append("<SPAN>" + lcsList.get(k) + " </SPAN>");
word1LastIndex = i + 1;
word2LastIndex = j + 1;
i = text1Words.length;
j = text2Words.length;
}
else if (!text1Words[i].equals(lcsList.get(k))) {
for (; i < text1Words.length &&
!text1Words[i].equals(lcsList.get(k)); i++) {
stringBuffer.append("<SPAN style='BACKGROUND-COLOR:" +
deleteColor + "'>" + text1Words[i] + " </SPAN>");
}
} else if (!text2Words[j].equals(lcsList.get(k))) {
for (; j < text2Words.length &&
!text2Words[j].equals(lcsList.get(k)), j++) {
stringBuffer.append("<SPAN style='BACKGROUND-COLOR:" +
insertColor + "'>" + text2Words[j] + " </SPAN>");
}
}
}
}
for (; word1LastIndex < text1Words.length; word1LastIndex++) {
stringBuffer.append("<SPAN style='BACKGROUND-COLOR:" +
deleteColor + "'>" + text1Words[word1LastIndex] + " </SPAN>");
}
for (; word2LastIndex < text2Words.length; word2LastIndex++) {
stringBuffer.append("<SPAN style='BACKGROUND-COLOR:" +
insertColor + "'>" + text2Words[word2LastIndex] + " </SPAN>");
}
}
return stringBuffer.toString();
}
}
Comparison (grammar)
Implementation
HTML
Framework
Vaadin
Mark (designation)
Space (architecture)
Algorithm
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