CaesarCipher: reduce amount of code, add test case, add YT link

andrei-punko · Dec 26, 2024 · 0813f98 · 0813f98
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Showing 3 changed files with 20 additions and 21 deletions.
diff --git a/README.md b/README.md
@@ -259,6 +259,7 @@ they contain enough code which describes implementation in a natural way.
 | Как скачать видео с Boosty                                                                       | [Youtube](https://youtu.be/b3ox1_xEx4U) | [Boosty](https://boosty.to/andd3dfx)                                                                                                                                                |
 | Прохождение теста подтверждения практического навыка "средний" по Java на hh.ru                  | [Youtube](https://youtu.be/ja4nLzZSj3s) | -                                                                                                                                                                                   |
 | Прохождение теста подтверждения практического навыка "продвинутый" по Java на hh.ru              | [Youtube](https://youtu.be/ce3g0nIJl24) | -                                                                                                                                                                                   |
+| Декодирование шифра Цезаря                                                                       | [Youtube](https://youtu.be/pjQ9sYo5bVE) | [Code](src/main/java/by/andd3dfx/string/CaesarCipher.java)                                                                                                                          |
 
 ## Materials & notes
 

diff --git a/src/main/java/by/andd3dfx/string/CaesarCipher.java b/src/main/java/by/andd3dfx/string/CaesarCipher.java
@@ -36,42 +36,38 @@
  * Выходные данные:
  * это яблоко красное
  * </pre>
+ *
+ * @see <a href="https://youtu.be/pjQ9sYo5bVE">Video solution</a>
  */
 public class CaesarCipher {
 
     // Русский алфавит
     private static final String ALPHABET = "абвгдеёжзийклмнопрстуфхцчшщъыьэюя";
 
     public String encode(String text, int shift) {
-        var words = text.split(" ");
-        return Arrays.stream(words)
-                .map(word -> encodeWord(word, shift))
-                .collect(Collectors.joining(" "));
+        return encodeWordWithSpacesSupport(text, shift);
     }
 
-    private String encodeWord(String text, int shift) {
-        var chars = text.toCharArray();
-        for (var i = 0; i < chars.length; i++) {
-            var targetIndex = ALPHABET.indexOf(chars[i]) + shift;
-            targetIndex %= ALPHABET.length();
-            chars[i] = ALPHABET.charAt(targetIndex);
-        }
-        return new String(chars);
+    public String decode(String text, int shift) {
+        return encodeWordWithSpacesSupport(text, -shift);
     }
 
-    public String decode(String encryptedText, int shift) {
-        var words = encryptedText.split(" ");
+    private String encodeWordWithSpacesSupport(String text, int shift) {
+        var words = text.split(" ");
         return Arrays.stream(words)
-                .map(word -> decodeWord(word, shift))
+                .map(word -> encodeWord(word, shift))
                 .collect(Collectors.joining(" "));
     }
 
-    private String decodeWord(String encryptedText, int shift) {
-        var chars = encryptedText.toCharArray();
+    private String encodeWord(String word, int shift) {
+        var chars = word.toCharArray();
         for (var i = 0; i < chars.length; i++) {
-            var targetIndex = ALPHABET.indexOf(chars[i]) - shift + ALPHABET.length();
-            targetIndex %= ALPHABET.length();
-            chars[i] = ALPHABET.charAt(targetIndex);
+            var index = ALPHABET.indexOf(chars[i]) + shift;
+            while (index < 0) {
+                index += ALPHABET.length();
+            }
+            index %= ALPHABET.length();
+            chars[i] = ALPHABET.charAt(index);
         }
         return new String(chars);
     }

diff --git a/src/test/java/by/andd3dfx/string/CaesarCipherTest.java b/src/test/java/by/andd3dfx/string/CaesarCipherTest.java
@@ -16,13 +16,15 @@ public void setUp() throws Exception {
 
     @Test
     public void encode() {
+        assertThat(caesarCipher.encode("андрей", 0)).isEqualTo("андрей");
         assertThat(caesarCipher.encode("абвгде", 1)).isEqualTo("бвгдеё");
         assertThat(caesarCipher.encode("это яблоко красное", 7)).isEqualTo("дщх ёзтхсх счжшфхл");
     }
 
     @Test
     public void decode() {
+        assertThat(caesarCipher.decode("андрей", 0)).isEqualTo("андрей");
         assertThat(caesarCipher.decode("бвгдеё", 1)).isEqualTo("абвгде");
         assertThat(caesarCipher.decode("дщх ёзтхсх счжшфхл", 7)).isEqualTo("это яблоко красное");
     }
-}
+}