kmp java implement--转

http://cs.nyu.edu/~yap/classes/basic/progs/patternMatching/KMP.java

/**
  * @file    KMP.java
  * @synopsis     An implementation of KMP matching, derived from
  *        a modification of the Match.java program.
  *        Again, the goal is to find an occurrence of a pattern P in a text T.
  *        CONVENTION:
  *        The first index (i=0) of arrays are not used.
  *
  * @author    Chee Yap
  * @date    Apr 25, 2001 (for Basic Algorithms class)
  */

public class KMP {

  // Members:
    char[] T;    // This is the text
     char[] P;    // This is pattern
    int [] fail;    // Failure function for pattern

  // Constructors:

    KMP(char[] p, char[] t) {
      P = p; T = t;
      computeFail();
    } //

  // Methods:

    /******************************************************
     Routine to compute the failure function
     ******************************************************/
    public void computeFail() {
      // init:
        fail = new int[P.length];
        fail[1] = 0;
      // loop:
        for (int k=2; k< fail.length; k++) {
          int kk = fail[k-1];
          while (kk>0 && (P[kk] != P[k-1]))
            kk = fail[kk];
          fail[k] = 1 + kk;
        }
    } // computeFail(P)

    /******************************************************
     THIS IS THE MAIN ROUTINE
     ******************************************************/
    public int find(int start) {
      // init:
        int j = start; // text index
        int k = 1; // pattern index
      // loop:
        while (j < T.length) {
          if (k >= P.length) return(j - k + 1);
          if ((T[j] == P[k]) || (k==0)) {
            j++; k++;
          } else {
            k = fail[k];    // k could become 0
          }
        } // while
      // Not found:
        return(-1);
    } // find()

    /******************************************************
     prints data
     ******************************************************/
    void output() {
      System.out.print("> Pattern = \"");
      for (int i=1; i< P.length; i++)
        System.out.print(P[i]);
      System.out.print("\"\n> Text    = \"");
      for (int i=1; i< T.length; i++)
        System.out.print(T[i]);
      System.out.println("\"");
    } // output()

    /******************************************************
     Main method
     ******************************************************/
    public static void main( String[] args) {

      // sample input with 6 keys
      //    (the first is a dummy key)

      // char[] p = {'0', 'o', 'u'};
      char[] p = {'0', 'y', 'o', 'u'};
      char[] t = {'0',
        'a', 'r', 'e', ' ', 'y', 'o', 'u', ' ',
        'a', ' ', 'y', 'o', 'u', 't', 'h', '?'};

      // construct a KMP object
      KMP m = new KMP(p, t);
      m.output();      // print data

      // find all matches
      int f = m.find(1);
      if (f<1)
          System.out.println(">>  No match found");
      else {
        while (f>=1) {
          System.out.println(">>  Match found at position " + f);
          f = m.find(f+1);
        }//while
      }//else
      } // main

}//class KMP