net.minidev.util.KMPMatch Maven / Gradle / Ivy
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package net.minidev.util;
/**
* Knuth-Morris-Pratt Algorithm for Pattern Matching
*/
public class KMPMatch {
/**
* Finds the first occurrence of the pattern in the text.
*/
public static int indexOf(byte[] data, byte[] pattern) {
int[] failure = computeFailure(pattern);
int j = 0;
if (data.length == 0) return -1;
for (int i = 0; i < data.length; i++) {
while (j > 0 && pattern[j] != data[i]) {
j = failure[j - 1];
}
if (pattern[j] == data[i]) { j++; }
if (j == pattern.length) {
return i - pattern.length + 1;
}
}
return -1;
}
/**
* Computes the failure function using a boot-strapping process,
* where the pattern is matched against itself.
*/
private static int[] computeFailure(byte[] pattern) {
int[] failure = new int[pattern.length];
int j = 0;
for (int i = 1; i < pattern.length; i++) {
while (j > 0 && pattern[j] != pattern[i]) {
j = failure[j - 1];
}
if (pattern[j] == pattern[i]) {
j++;
}
failure[i] = j;
}
return failure;
}
}