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code-clean-up (#4519)

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* code-clean-up

* style: make `RabinKarpAlgorithm` a proper utility class

---------

Co-authored-by: arintripathi1 <arint@trainee.nrifintech.com>
Co-authored-by: vil02 <vil02@o2.pl>
Co-authored-by: Piotr Idzik <65706193+vil02@users.noreply.github.com>
This commit is contained in:
Arin
2023-10-03 23:02:59 +05:30
committed by GitHub
parent 535230acae
commit 4fab7adfaa
2 changed files with 33 additions and 37 deletions
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67
src/main/java/com/thealgorithms/searches/RabinKarpAlgorithm.java
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@ -1,50 +1,48 @@
package com.thealgorithms.searches;
// Following program is a Java implementation
// of Rabin Karp Algorithm given in the CLRS book
// Implementation of Rabin Karp Algorithm
public class RabinKarpAlgorithm {
public final class RabinKarpAlgorithm {
private RabinKarpAlgorithm() {
}
// d is the number of characters in the input alphabet
public static final int d = 256;
private static final int d = 256;
/* pat -> pattern
txt -> text
q -> A prime number
*/
public int search(String pat, String txt, int q) {
int index = -1; // note: -1 here represent not found, it is not an index
int M = pat.length();
int N = txt.length();
int i, j;
int p = 0; // hash value for pattern
int t = 0; // hash value for txt
public static int search(String pattern, String text, int primeNumber) {
int index = -1; // -1 here represents not found
int patternLength = pattern.length();
int textLength = text.length();
int hashForPattern = 0;
int hashForText = 0;
int h = 1;
// The value of h would be "pow(d, M-1)%q"
for (i = 0; i < M - 1; i++) h = (h * d) % q;
// The value of h would be "pow(d, patternLength-1)%primeNumber"
for (int i = 0; i < patternLength - 1; i++) h = (h * d) % primeNumber;
// Calculate the hash value of pattern and first
// window of text
for (i = 0; i < M; i++) {
p = (d * p + pat.charAt(i)) % q;
t = (d * t + txt.charAt(i)) % q;
for (int i = 0; i < patternLength; i++) {
hashForPattern = (d * hashForPattern + pattern.charAt(i)) % primeNumber;
hashForText = (d * hashForText + text.charAt(i)) % primeNumber;
}
// Slide the pattern over text one by one
for (i = 0; i <= N - M; i++) {
// Check the hash values of current window of text
// and pattern. If the hash values match then only
// check for characters one by one
if (p == t) {
for (int i = 0; i <= textLength - patternLength; i++) {
/* Check the hash values of current window of text
and pattern. If the hash values match then only
check for characters one by one*/
int j = 0;
if (hashForPattern == hashForText) {
/* Check for characters one by one */
for (j = 0; j < M; j++) {
if (txt.charAt(i + j) != pat.charAt(j)) break;
for (j = 0; j < patternLength; j++) {
if (text.charAt(i + j) != pattern.charAt(j)) break;
}
// if p == t and pat[0...M-1] = txt[i, i+1, ...i+M-1]
if (j == M) {
System.out.println("Pattern found at index " + i);
// if hashForPattern == hashForText and pattern[0...patternLength-1] = text[i, i+1, ...i+patternLength-1]
if (j == patternLength) {
index = i;
return index;
}
@ -52,12 +50,11 @@ public class RabinKarpAlgorithm {
// Calculate hash value for next window of text: Remove
// leading digit, add trailing digit
if (i < N - M) {
t = (d * (t - txt.charAt(i) * h) + txt.charAt(i + M)) % q;
if (i < textLength - patternLength) {
hashForText = (d * (hashForText - text.charAt(i) * h) + text.charAt(i + patternLength)) % primeNumber;
// We might get negative value of t, converting it
// to positive
if (t < 0) t = (t + q);
// handling negative hashForText
if (hashForText < 0) hashForText = (hashForText + primeNumber);
}
}
return index; // return -1 if pattern does not found