kmp java implement--转

/**
* @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