SuffixStringMatcher.java

/**
 * Copyright 2008 - CommonCrawl Foundation
 * 
 *    This program 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.
 *
 *    This program 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 this program.  If not, see <http://www.gnu.org/licenses/>.
 *
 **/

package org.commoncrawl.util;

import java.util.Collection;
import java.util.Iterator;

/**
 * A class for efficiently matching <code>String</code>s against a set of
 * suffixes. Zero-length <code>Strings</code> are ignored.
 */
public class SuffixStringMatcher extends TrieStringMatcher {

  /**
   * Creates a new <code>PrefixStringMatcher</code> which will match
   * <code>String</code>s with any suffix in the supplied array.
   */
  public SuffixStringMatcher(String[] suffixes) {
    super();
    for (int i = 0; i < suffixes.length; i++)
      addPatternBackward(suffixes[i]);
  }

  /**
   * Creates a new <code>PrefixStringMatcher</code> which will match
   * <code>String</code>s with any suffix in the supplied
   * <code>Collection</code>
   */
  public SuffixStringMatcher(Collection suffixes) {
    super();
    Iterator iter = suffixes.iterator();
    while (iter.hasNext())
      addPatternBackward((String) iter.next());
  }

  /**
   * Returns true if the given <code>String</code> is matched by a suffix in the
   * trie
   */
  public boolean matches(String input) {
    TrieNode node = root;
    for (int i = input.length() - 1; i >= 0; i--) {
      node = node.getChild(input.charAt(i));
      if (node == null)
        return false;
      if (node.isTerminal())
        return true;
    }
    return false;
  }

  /**
   * Returns the shortest suffix of <code>input<code> that is matched,
   * or <code>null<code> if no match exists.
   */
  public String shortestMatch(String input) {
    TrieNode node = root;
    for (int i = input.length() - 1; i >= 0; i--) {
      node = node.getChild(input.charAt(i));
      if (node == null)
        return null;
      if (node.isTerminal())
        return input.substring(i);
    }
    return null;
  }

  /**
   * Returns the longest suffix of <code>input<code> that is matched,
   * or <code>null<code> if no match exists.
   */
  public String longestMatch(String input) {
    TrieNode node = root;
    String result = null;
    for (int i = input.length() - 1; i >= 0; i--) {
      node = node.getChild(input.charAt(i));
      if (node == null)
        break;
      if (node.isTerminal())
        result = input.substring(i);
    }
    return result;
  }
  
  /** Returns true if an exact match is found 
   * 
   * @param argv
   */
  public boolean exactMatch(String input) { 
    TrieNode node = root;
    for (int i = input.length() - 1; i >= 0; i--) {
      node = node.getChild(input.charAt(i));
      if (node == null)
        break;
      if (i== 0 && node.isTerminal()) { 
        return true;
      }
    }
    return false;    
  }

  public static final void main(String[] argv) {
    SuffixStringMatcher matcher = new SuffixStringMatcher(new String[] { "a",
        "abcd", "bcd", "bcdefg", "defg", "aac", "baz", "foo", "foobar" });

    String[] tests = { "a", "ac", "abcd", "abcdefg", "apple", "aa", "aac",
        "aaccca", "abaz", "baz", "bazooka", "fo", "foobar", "kite", };

    for (int i = 0; i < tests.length; i++) {
      System.out.println("testing: " + tests[i]);
      System.out.println("   matches: " + matcher.matches(tests[i]));
      System.out.println("  shortest: " + matcher.shortestMatch(tests[i]));
      System.out.println("   longest: " + matcher.longestMatch(tests[i]));

    }
    System.out.println("   exact: " + matcher.exactMatch("foobar"));
    System.out.println("   not exact: " + matcher.exactMatch("fooba"));
    System.out.println("   not exact: " + matcher.exactMatch("foobarz"));
    System.out.println("   exact: " + matcher.exactMatch("foo"));

  }
}