org.zodiac.algorithms.strings.KnuthMorrisPratt Maven / Gradle / Ivy
package org.zodiac.algorithms.strings;
import java.util.ArrayList;
import java.util.List;
/**
* This class implements KMP algorithm for finding length of maximal prefix-suffix for each prefix of the string.
* Prefix-suffix of string S is a substring which occurs at the beginning and at the end of S.
*
* Time complexity: O(n)
*
* @see Knuth Morris Pratt (Wikipedia)
*
*
*/
public abstract class KnuthMorrisPratt {
private KnuthMorrisPratt() {}
/**
* This function implements KMP algorithm for finding length of maximal prefix-suffix for each prefix of the string.
* Prefix-suffix of string S is a substring which occurs at the beginning and at the end of S.
*
* @param text Text
* @return maximal length of prefix-suffix for each prefix of the string text
*/
public static List getPrefSufTable(String text) {
final List prefSufTable = new ArrayList();
final char[] chars = text.toCharArray();
if (text.length() == 0)
return prefSufTable;
prefSufTable.add(0);
for (int i = 1; i 0 && (chars[i] != chars[sizeOfPrefSuf]))
/*Because string is 0-indexed.*/
sizeOfPrefSuf = prefSufTable.get(sizeOfPrefSuf-1);
/*
* If characters at this positions are different then sizeOfPrefSuf is equal to zero,
* so there is no proper prefix-suffix.
* */
if (chars[i] == chars[sizeOfPrefSuf]) {
prefSufTable.add(sizeOfPrefSuf+1);
} else {
prefSufTable.add(0);
}
}
return prefSufTable;
}
}