Soundex算法

/**  
* Soundex - the Soundex Algorithm, as described by Knuth  
* <p>  
* This class implements the soundex algorithm as described by Donald  
* Knuth in Volume 3 of <I>The Art of Computer Programming</I>.  The  
* algorithm is intended to hash words (in particular surnames) into  
* a small space using a simple model which approximates the sound of  
* the word when spoken by an English speaker.  Each word is reduced  
* to a four character string, the first character being an upper case  
* letter and the remaining three being digits. Double letters are  
* collapsed to a single digit.  
*   
* <h2>EXAMPLES</h2>  
* Knuth's examples of various names and the soundex codes they map  
* to are:  
* <b>Euler, Ellery -> E460  
* <b>Gauss, Ghosh -> G200  
* <b>Hilbert, Heilbronn -> H416  
* <b>Knuth, Kant -> K530  
* <b>Lloyd, Ladd -> L300  
* <b>Lukasiewicz, Lissajous -> L222  
*   
* <h2>LIMITATIONS</h2>  
* As the soundex algorithm was originally used a <B>long</B> time ago  
* in the United States of America, it uses only the English alphabet  
* and pronunciation.  
* <p>  
* As it is mapping a large space (arbitrary length strings) onto a  
* small space (single letter plus 3 digits) no inference can be made  
* about the similarity of two strings which end up with the same  
* soundex code.  For example, both "Hilbert" and "Heilbronn" end up  
* with a soundex code of "H416".  
* <p>  
* The soundex() method is static, as it maintains no per-instance  
* state; this means you never need to instantiate this class.  
*  
* @author Perl implementation by Mike Stok (<[e-mail]>) from  
* the description given by Knuth.  Ian Phillips (<[e-mail]>) and  
* Rich Pinder (<[e-mail]>) supplied ideas and spotted  
* mistakes.  
* @author Ian Darwin, http://www.darwinsys.com/ (Java Version)  
* @version $Id: Soundex.java,v 1.9 2004/02/23 00:30:49 ian Exp $  
*/  
public class Soundex {   
  
  /* Implements the mapping  
   * from: AEHIOUWYBFPVCGJKQSXZDTLMNR  
   * to:   00000000111122222222334556  
   */  
  public static final char[] MAP = {   
    //A  B   C   D   E   F   G   H   I   J   K   L   M   
    '0','1','2','3','0','1','2','0','0','2','2','4','5',   
    //N  O   P   W   R   S   T   U   V   W   X   Y   Z   
    '5','0','1','2','6','2','3','0','1','0','2','0','2'  
  };   
  
  /** Convert the given String to its Soundex code.  
   * @return null If the given string can't be mapped to Soundex.  
   */  
  public static String soundex(String s) {   
  
    // Algorithm works on uppercase (mainframe era).   
    String t = s.toUpperCase();   
  
    StringBuffer res = new StringBuffer();   
    char c, prev = '?';   
  
    // Main loop: find up to 4 chars that map.   
    for (int i=0; i<t.length() && res.length() < 4 &&   
      (c = t.charAt(i)) != ','; i++) {   
  
      // Check to see if the given character is alphabetic.   
      // Text is already converted to uppercase. Algorithm   
      // only handles ASCII letters, do NOT use Character.isLetter()!   
      // Also, skip double letters.   
      if (c>='A' && c<='Z' && c != prev) {   
        prev = c;   
  
        // First char is installed unchanged, for sorting.   
        if (i==0)   
          res.append(c);   
        else {   
          char m = MAP[c-'A'];   
          if (m != '0')   
            res.append(m);   
        }   
      }   
    }   
    if (res.length() == 0)   
      return null;   
    for (int i=res.length(); i<4; i++)   
      res.append('0');   
    return res.toString();   
  }   
  /** main */  
  public static void main(String[] args) {    
    String[] names = {   
      "Darwin, Ian",   
      "Davidson, Greg",   
      "Darwent, William",   
      "Derwin, Daemon"  
    };   
    for (int i = 0; i< names.length; i++)   
      System.out.println(Soundex.soundex(names[i]) + ' ' + names[i]);   
  }   
  
}