edu.princeton.cs.algs4.LongestRepeatedSubstring Maven / Gradle / Ivy
/******************************************************************************
* Compilation: javac LongestRepeatedSubstring.java
* Execution: java LongestRepeatedSubstring < file.txt
* Dependencies: StdIn.java SuffixArray.java
* Data files: https://algs4.cs.princeton.edu/63suffix/tale.txt
* https://algs4.cs.princeton.edu/63suffix/tinyTale.txt
* https://algs4.cs.princeton.edu/63suffix/mobydick.txt
*
* Reads a text string from stdin, replaces all consecutive blocks of
* whitespace with a single space, and then computes the longest
* repeated substring in that text using a suffix array.
*
* % java LongestRepeatedSubstring < tinyTale.txt
* 'st of times it was the '
*
* % java LongestRepeatedSubstring < mobydick.txt
* ',- Such a funny, sporty, gamy, jesty, joky, hoky-poky lad, is the Ocean, oh! Th'
*
* % java LongestRepeatedSubstring
* aaaaaaaaa
* 'aaaaaaaa'
*
* % java LongestRepeatedSubstring
* abcdefg
* ''
*
******************************************************************************/
package edu.princeton.cs.algs4;
/**
* The {@code LongestRepeatedSubstring} class provides a {@link SuffixArray}
* client for computing the longest repeated substring of a string that
* appears at least twice. The repeated substrings may overlap (but must
* be distinct).
*
* For additional documentation,
* see Section 6.3 of
* Algorithms, 4th Edition by Robert Sedgewick and Kevin Wayne.
*
* See also {@link LongestCommonSubstring}.
*
* @author Robert Sedgewick
* @author Kevin Wayne
*/
public class LongestRepeatedSubstring {
// Do not instantiate.
private LongestRepeatedSubstring() { }
/**
* Returns the longest common string of the two specified strings.
*
* @param s one string
* @param t the other string
* @return the longest common string that appears as a substring
*/
/**
* Returns the longest repeated substring of the specified string.
*
* @param text the string
* @return the longest repeated substring that appears in {@code text};
* the empty string if no such string
*/
public static String lrs(String text) {
int n = text.length();
SuffixArray sa = new SuffixArray(text);
String lrs = "";
for (int i = 1; i < n; i++) {
int length = sa.lcp(i);
if (length > lrs.length()) {
// lrs = sa.select(i).substring(0, length);
lrs = text.substring(sa.index(i), sa.index(i) + length);
}
}
return lrs;
}
/**
* Unit tests the {@code lrs()} method.
*
* @param args the command-line arguments
*/
public static void main(String[] args) {
String text = StdIn.readAll().replaceAll("\\s+", " ");
StdOut.println("'" + lrs(text) + "'");
}
}
/******************************************************************************
* Copyright 2002-2018, Robert Sedgewick and Kevin Wayne.
*
* This file is part of algs4.jar, which accompanies the textbook
*
* Algorithms, 4th edition by Robert Sedgewick and Kevin Wayne,
* Addison-Wesley Professional, 2011, ISBN 0-321-57351-X.
* http://algs4.cs.princeton.edu
*
*
* algs4.jar is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* algs4.jar is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with algs4.jar. If not, see http://www.gnu.org/licenses.
******************************************************************************/