knuth morris pratt algorithm

Author: amitbansal7

17. Substring Search/BruteForce.java

@@ -0,0 +1,23 @@
+import java.util.Scanner;
+
+public class BruteForce {
+	public static void main(String[] args) {
+		String text = "abcklmndefghklmnijklmnopqrsklmntuvwxyz";
+		String pattern = "klmno";
+		// time : O(M*N)
+		for (int i = 0; i < text.length(); i++) {
+			int j;
+			for (j = 0; j < pattern.length(); j++) {
+				if (text.charAt(i + j) != pattern.charAt(j))
+					break;
+			}
+
+			if (j == pattern.length()) {
+				System.out.println("Starting index : " + i);
+				return;
+			}
+		}
+
+		System.out.println("Not found");
+	}
+}

17. Substring Search/KnuthMorrisPratt.java

@@ -0,0 +1,51 @@
+public class KnuthMorrisPratt {
+
+	public static int[] ComputeTempArray(String pattern) {
+		int[] lps = new int[pattern.length()];
+		int idx = 0;
+
+		for (int i = 1; i < pattern.length();) {
+			if (pattern.charAt(i) == pattern.charAt(idx)) {
+				lps[i] = idx + 1;
+				idx++;
+				i++;
+			} else {
+				if (idx != 0) {
+					idx = lps[idx - 1];
+				} else {
+					lps[i] = 0;
+					i++;
+				}
+			}
+		}
+		return lps;
+	}
+
+	public static void main(String[] args) {
+		String text = "abcxabcdabcdabcaabcdabcyjjklqw";
+		String pattern = "abcdabcy";
+
+		int[] lps = ComputeTempArray(pattern);
+
+		int i = 0, j = 0;
+		while (i < text.length() && j < pattern.length()) {
+			if (text.charAt(i) == pattern.charAt(j)) {
+				i++;
+				j++;
+			} else {
+				if (j != 0) {
+					j = lps[j - 1];
+				} else {
+					i++;
+				}
+			}
+
+			if (j == pattern.length()) {
+				System.out.println("Starting index : " + (i - j));
+				return;
+			}
+		}
+
+		System.out.println("Not found");
+	}
+}