Add Ex 22.4

Author: jsquared21

Exercise_22/Exercise_22_04/Exercise_22_04.class

@@ -0,0 +1,49 @@
+/*********************************************************************************
+* (Pattern matching) Write a program that prompts the user to enter two strings  *
+* and tests whether the second string is a substring of the first string. (Don’t *
+* use the indexOf method in the String class.) Analyze the time complexity of    *
+* your algorithm.                                                                *
+*********************************************************************************/
+import java.util.Scanner;
+
+public class Exercise_22_04 {
+	public static void main(String[] args) {
+		Scanner input = new Scanner(System.in);
+
+		// Prompt the user to enter two strings
+		System.out.print("Enter a string s1: ");
+		String s1 = input.nextLine();
+		System.out.print("Enter a string s2: ");
+		String s2 = input.nextLine();
+
+		int index = -1; // Index of sub string
+		int count = 0; // Count matching characters
+		boolean matched = false; 
+
+		// tests whether the second string 
+		// is a substring of the first string
+		for (int i = 0; i < s1.length(); i++) {
+			if (s1.charAt(i) != s2.charAt(count)){
+				count = 0;
+			}
+
+			if (s1.charAt(i) == s2.charAt(count)) {
+				if (count == 0) 
+					index = i;	 
+				count++;
+			}
+
+			if (count == s2.length()) {
+				matched = true;
+				break;
+			}
+		}
+
+		// Display result
+		if (matched)
+			System.out.println("matched at index " + index);
+		else
+			System.out.println("\"" + s2 + 
+				"\" is not a substring of \"" + s1 + "\""+ ".");
+	}
+}