refactor: change packages (#5430)

* refactor: change package * refactor: fix name --------- Co-authored-by: alxkm <alx@alx.com>
2025-12-19 07:00:35 +08:00 · 2024-08-30 11:58:24 +02:00
parent f8ff6af893
commit b0de93b3ce
10 changed files with 13 additions and 13 deletions
--- a/src/main/java/com/thealgorithms/strings/RabinKarp.java
+++ b/src/main/java/com/thealgorithms/strings/RabinKarp.java
@@ -0,0 +1,82 @@
+package com.thealgorithms.strings;
+
+import java.util.Scanner;
+
+/**
+ * @author Prateek Kumar Oraon (https://github.com/prateekKrOraon)
+ *
+ An implementation of Rabin-Karp string matching algorithm
+ Program will simply end if there is no match
+ */
+public final class RabinKarp {
+    private RabinKarp() {
+    }
+
+    public static Scanner scanner = null;
+    public static final int ALPHABET_SIZE = 256;
+
+    public static void main(String[] args) {
+        scanner = new Scanner(System.in);
+        System.out.println("Enter String");
+        String text = scanner.nextLine();
+        System.out.println("Enter pattern");
+        String pattern = scanner.nextLine();
+
+        int q = 101;
+        searchPat(text, pattern, q);
+    }
+
+    private static void searchPat(String text, String pattern, int q) {
+        int m = pattern.length();
+        int n = text.length();
+        int t = 0;
+        int p = 0;
+        int h = 1;
+        int j = 0;
+        int i = 0;
+
+        h = (int) Math.pow(ALPHABET_SIZE, m - 1) % q;
+
+        for (i = 0; i < m; i++) {
+            // hash value is calculated for each character and then added with the hash value of the
+            // next character for pattern as well as the text for length equal to the length of
+            // pattern
+            p = (ALPHABET_SIZE * p + pattern.charAt(i)) % q;
+            t = (ALPHABET_SIZE * t + text.charAt(i)) % q;
+        }
+
+        for (i = 0; i <= n - m; i++) {
+            // if the calculated hash value of the pattern and text matches then
+            // all the characters of the pattern is matched with the text of length equal to length
+            // of the pattern if all matches then pattern exist in string if not then the hash value
+            // of the first character of the text is subtracted and hash value of the next character
+            // after the end of the evaluated characters is added
+            if (p == t) {
+                // if hash value matches then the individual characters are matched
+                for (j = 0; j < m; j++) {
+                    // if not matched then break out of the loop
+                    if (text.charAt(i + j) != pattern.charAt(j)) {
+                        break;
+                    }
+                }
+
+                // if all characters are matched then pattern exist in the string
+                if (j == m) {
+                    System.out.println("Pattern found at index " + i);
+                }
+            }
+
+            // if i<n-m then hash value of the first character of the text is subtracted and hash
+            // value of the next character after the end of the evaluated characters is added to get
+            // the hash value of the next window of characters in the text
+            if (i < n - m) {
+                t = (ALPHABET_SIZE * (t - text.charAt(i) * h) + text.charAt(i + m)) % q;
+
+                // if hash value becomes less than zero than q is added to make it positive
+                if (t < 0) {
+                    t = (t + q);
+                }
+            }
+        }
+    }
+}