Algorithms/JavaAlgorithms
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The function had cryptic variable names. Now it's more readable.

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This commit is contained in:
_0 2018-10-15 11:52:08 +03:00
parent c6e6610909
commit 1177b54746
1 changed files with 16 additions and 18 deletions
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32
Others/KMP.java
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@ -1,25 +1,26 @@
/*
Implementation of Knuth–Morris–Pratt algorithm
Usage:
final String T = "AAAAABAAABA";
final String P = "AAAA";
KMPmatcher(T, P);
Usage: see the main function for an example
*/
public class KMP {
// find the starting index in string T[] that matches the search word P[]
public void KMPmatcher(final String T, final String P) {
final int m = T.length();
final int n = P.length();
final int[] pi = computePrefixFunction(P);
//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 && T.charAt(i) != P.charAt(q)) {
while (q > 0 && haystack.charAt(i) != needle.charAt(q)) {
q = pi[q - 1];
}
if (T.charAt(i) == P.charAt(q)) {
if (haystack.charAt(i) == needle.charAt(q)) {
q++;
}
@ -28,11 +29,9 @@ public class KMP {
q = pi[q - 1];
}
}
}
// return the prefix function
private int[] computePrefixFunction(final String P) {
private static int[] computePrefixFunction(final String P) {
final int n = P.length();
final int[] pi = new int[n];
pi[0] = 0;
@ -49,7 +48,6 @@ public class KMP {
pi[i] = q;
}
return pi;
}
}