53 lines
1.6 KiB
Java
53 lines
1.6 KiB
Java
/*
|
||
Implementation of Knuth–Morris–Pratt algorithm
|
||
Usage: see the main function for an example
|
||
*/
|
||
public class KMP {
|
||
//a working example
|
||
public static void main(String[] args) {
|
||
final String haystack = "AAAAABAAABA"; //This is the full string
|
||
final String needle = "AAAA"; //This is the substring that we want to find
|
||
KMPmatcher(haystack, needle);
|
||
}
|
||
// find the starting index in string haystack[] that matches the search word P[]
|
||
public static void KMPmatcher(final String haystack, final String needle) {
|
||
final int m = haystack.length();
|
||
final int n = needle.length();
|
||
final int[] pi = computePrefixFunction(needle);
|
||
int q = 0;
|
||
for (int i = 0; i < m; i++) {
|
||
while (q > 0 && haystack.charAt(i) != needle.charAt(q)) {
|
||
q = pi[q - 1];
|
||
}
|
||
|
||
if (haystack.charAt(i) == needle.charAt(q)) {
|
||
q++;
|
||
}
|
||
|
||
if (q == n) {
|
||
System.out.println("Pattern starts: " + (i + 1 - n));
|
||
q = pi[q - 1];
|
||
}
|
||
}
|
||
}
|
||
// return the prefix function
|
||
private static int[] computePrefixFunction(final String P) {
|
||
final int n = P.length();
|
||
final int[] pi = new int[n];
|
||
pi[0] = 0;
|
||
int q = 0;
|
||
for (int i = 1; i < n; i++) {
|
||
while (q > 0 && P.charAt(q) != P.charAt(i)) {
|
||
q = pi[q - 1];
|
||
}
|
||
|
||
if (P.charAt(q) == P.charAt(i)) {
|
||
q++;
|
||
}
|
||
|
||
pi[i] = q;
|
||
|
||
}
|
||
return pi;
|
||
}
|
||
} |