diff --git a/Algorithms/KMPAlgorithm.java b/Algorithms/KMPAlgorithm.java new file mode 100644 index 0000000..88cc795 --- /dev/null +++ b/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(); + } +}