Merge pull request #25 from coddingjatin/main

Added KMP Algorithm In Java

Author: IamBisrutPyne

Algorithms/KMPAlgorithm.java

@@ -0,0 +1,95 @@
+// KMP Algorithm in Java
+// ------------------------------------------------------
+// Author: Jatin Vishwakarma
+// Description: Implementation of the Knuth–Morris–Pratt (KMP)
+// Pattern Searching Algorithm in Java.
+// This algorithm efficiently finds all occurrences of a pattern
+// in a given text with O(n + m) time complexity.
+
+import java.util.Scanner;
+
+public class KMPAlgorithm {
+
+    // Function to preprocess the pattern and build the LPS (Longest Prefix Suffix) array
+    private static void computeLPSArray(String pattern, int[] lps) {
+        int length = 0;  // length of the previous longest prefix suffix
+        int i = 1;
+        lps[0] = 0;  // LPS of the first character is always 0
+
+        // Loop to calculate lps[i] for i = 1 to pattern.length - 1
+        while (i < pattern.length()) {
+            if (pattern.charAt(i) == pattern.charAt(length)) {
+                length++;
+                lps[i] = length;
+                i++;
+            } else {
+                if (length != 0) {
+                    // This is tricky — consider the example "AAACAAAA"
+                    length = lps[length - 1];
+                } else {
+                    lps[i] = 0;
+                    i++;
+                }
+            }
+        }
+    }
+
+    // KMP Search Function
+    public static void KMPSearch(String pattern, String text) {
+        int M = pattern.length();
+        int N = text.length();
+
+        // Create LPS array
+        int[] lps = new int[M];
+        computeLPSArray(pattern, lps);
+
+        int i = 0; // index for text[]
+        int j = 0; // index for pattern[]
+
+        boolean found = false;
+
+        while (i < N) {
+            if (pattern.charAt(j) == text.charAt(i)) {
+                i++;
+                j++;
+            }
+
+            if (j == M) {
+                System.out.println("✅ Pattern found at index: " + (i - j));
+                j = lps[j - 1];
+                found = true;
+            }
+
+            // Mismatch after j matches
+            else if (i < N && pattern.charAt(j) != text.charAt(i)) {
+                // Do not match lps[0..lps[j-1]] characters, they will match anyway
+                if (j != 0)
+                    j = lps[j - 1];
+                else
+                    i++;
+            }
+        }
+
+        if (!found)
+            System.out.println("❌ Pattern not found in the given text.");
+    }
+
+    public static void main(String[] args) {
+        Scanner sc = new Scanner(System.in);
+
+        System.out.println("=====================================");
+        System.out.println("   KMP STRING MATCHING ALGORITHM");
+        System.out.println("=====================================");
+        System.out.print("Enter the text: ");
+        String text = sc.nextLine();
+
+        System.out.print("Enter the pattern to search: ");
+        String pattern = sc.nextLine();
+
+        System.out.println("\n🔍 Searching for pattern...");
+        KMPSearch(pattern, text);
+
+        System.out.println("\n--- Program Completed Successfully ---");
+        sc.close();
+    }
+}