Change project structure to a Maven Java project + Refactor (#2816)

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

@@ -0,0 +1,62 @@
+package com.thealgorithms.ciphers;
+
+/**
+ * A Java implementation of Vigenere Cipher.
+ *
+ * @author straiffix
+ * @author beingmartinbmc
+ */
+public class Vigenere {
+
+    public static String encrypt(final String message, final String key) {
+
+        StringBuilder result = new StringBuilder();
+
+        for (int i = 0, j = 0; i < message.length(); i++) {
+            char c = message.charAt(i);
+            if (Character.isLetter(c)) {
+                if (Character.isUpperCase(c)) {
+                    result.append((char) ((c + key.toUpperCase().charAt(j) - 2 * 'A') % 26 + 'A'));
+
+                } else {
+                    result.append((char) ((c + key.toLowerCase().charAt(j) - 2 * 'a') % 26 + 'a'));
+                }
+            } else {
+                result.append(c);
+            }
+            j = ++j % key.length();
+        }
+        return result.toString();
+    }
+
+    public static String decrypt(final String message, final String key) {
+        StringBuilder result = new StringBuilder();
+
+        for (int i = 0, j = 0; i < message.length(); i++) {
+
+            char c = message.charAt(i);
+            if (Character.isLetter(c)) {
+                if (Character.isUpperCase(c)) {
+                    result.append((char) ('Z' - (25 - (c - key.toUpperCase().charAt(j))) % 26));
+
+                } else {
+                    result.append((char) ('z' - (25 - (c - key.toLowerCase().charAt(j))) % 26));
+                }
+            } else {
+                result.append(c);
+            }
+
+            j = ++j % key.length();
+        }
+        return result.toString();
+    }
+
+    public static void main(String[] args) {
+        String text = "Hello World!";
+        String key = "itsakey";
+        System.out.println(text);
+        String ciphertext = encrypt(text, key);
+        System.out.println(ciphertext);
+        System.out.println(decrypt(ciphertext, key));
+    }
+}