Update MonoAlphabetic.java

Author: riti2601

src/main/java/com/thealgorithms/ciphers/MonoAlphabetic.java

@@ -2,49 +2,63 @@
 
 public final class MonoAlphabetic {
 
-    private final String key;
-
-    // Constructor to initialize the key for encryption and decryption
-    public MonoAlphabetic(String key) {
-        this.key = key.toUpperCase(); // Store the key in uppercase to match the encryption/decryption logic
+    // Private constructor to prevent instantiation of utility class
+    private MonoAlphabetic() {
+        throw new UnsupportedOperationException("Utility class");
     }
 
     // Encryption method
-    public String encrypt(String data) {
-        StringBuilder sb = new StringBuilder(data.toUpperCase());
-
-        for (int i = 0; i < sb.length(); i++) {
-            char currentChar = sb.charAt(i);
-            if (Character.isLetter(currentChar)) { // Check if it's a letter
-                int index = currentChar - 'A'; // Get the index for the character
-                sb.setCharAt(i, key.charAt(index)); // Replace with the key character
+    public static String encrypt(String data, String key) {
+        StringBuilder sb = new StringBuilder();
+
+        // Convert to uppercase to match the key mapping
+        data = data.toUpperCase();
+
+        for (char c : data.toCharArray()) {
+            if (c >= 'A' && c <= 'Z') {
+                // Get the index (0-25) for the character
+                int idx = c - 'A';
+                // Append the character at the corresponding index in the key
+                sb.append(key.charAt(idx));
+            } else {
+                // If character is not A-Z, append it as is
+                sb.append(c);
             }
         }
         return sb.toString();
     }
 
     // Decryption method
-    public String decrypt(String data) {
-        StringBuilder sb = new StringBuilder(data.toUpperCase());
-
-        for (int i = 0; i < sb.length(); i++) {
-            char currentChar = sb.charAt(i);
-            if (Character.isLetter(currentChar)) { // Check if it's a letter
-                int index = key.indexOf(currentChar); // Find the character in the key
-                if (index != -1) {
-                    sb.setCharAt(i, (char) (index + 'A')); // Replace with the original character
+    public static String decrypt(String data, String key) {
+        StringBuilder sb = new StringBuilder();
+
+        // Convert to uppercase to match the key mapping
+        data = data.toUpperCase();
+
+        for (char c : data.toCharArray()) {
+            if (c >= 'A' && c <= 'Z') {
+                // Get the index from the key for the character
+                int idx = getIndex(c, key);
+                // Append the original character
+                if (idx != -1) {
+                    char originalChar = (char) (idx + 'A');
+                    sb.append(originalChar);
                 }
+            } else {
+                // If character is not A-Z, append it as is
+                sb.append(c);
             }
         }
         return sb.toString();
     }
 
-    // Static utility methods for encryption/decryption without creating an instance
-    public static String encrypt(String data, String key) {
-        return new MonoAlphabetic(key).encrypt(data);
-    }
-
-    public static String decrypt(String data, String key) {
-        return new MonoAlphabetic(key).decrypt(data);
+    // Helper method to get index of a character in the key
+    private static int getIndex(char c, String key) {
+        for (int i = 0; i < key.length(); i++) {
+            if (key.charAt(i) == c) {
+                return i; // Return the index if the character matches
+            }
+        }
+        return -1; // Return -1 if character not found (should not happen for valid inputs)
     }
 }