Resolve build errors & cleanup structure (#2334)

Ciphers/SimpleSubstitutionCipher.java

@@ -0,0 +1,83 @@
+package Ciphers;
+
+import java.util.*;
+
+/**
+ * The simple substitution cipher is a cipher that has been in use for many hundreds of years (an
+ * excellent history is given in Simon Singhs 'the Code Book'). It basically consists of
+ * substituting every plaintext character for a different ciphertext character. It differs from the
+ * Caesar cipher in that the cipher alphabet is not simply the alphabet shifted, it is completely
+ * jumbled.
+ *
+ * @author Hassan Elseoudy
+ */
+public class SimpleSubstitutionCipher {
+
+  /**
+   * Encrypt text by replacing each element with its opposite character.
+   *
+   * @return Encrypted message
+   */
+  public static String encode(String message, String cipherSmall) {
+    StringBuilder encoded = new StringBuilder();
+
+    // This map is used to encode
+    Map<Character, Character> cipherMap = new HashMap<>();
+
+    char beginSmallLetter = 'a';
+    char beginCapitalLetter = 'A';
+
+    cipherSmall = cipherSmall.toLowerCase();
+    String cipherCapital = cipherSmall.toUpperCase();
+
+    // To handle Small and Capital letters
+    for (int i = 0; i < cipherSmall.length(); i++) {
+      cipherMap.put(beginSmallLetter++, cipherSmall.charAt(i));
+      cipherMap.put(beginCapitalLetter++, cipherCapital.charAt(i));
+    }
+
+    for (int i = 0; i < message.length(); i++) {
+      if (Character.isAlphabetic(message.charAt(i))) encoded.append(cipherMap.get(message.charAt(i)));
+      else encoded.append(message.charAt(i));
+    }
+
+    return encoded.toString();
+  }
+
+  /**
+   * Decrypt message by replacing each element with its opposite character in cipher.
+   *
+   * @return message
+   */
+  public static String decode(String encryptedMessage, String cipherSmall) {
+    StringBuilder decoded = new StringBuilder();
+
+    Map<Character, Character> cipherMap = new HashMap<>();
+
+    char beginSmallLetter = 'a';
+    char beginCapitalLetter = 'A';
+
+    cipherSmall = cipherSmall.toLowerCase();
+    String cipherCapital = cipherSmall.toUpperCase();
+
+    for (int i = 0; i < cipherSmall.length(); i++) {
+      cipherMap.put(cipherSmall.charAt(i), beginSmallLetter++);
+      cipherMap.put(cipherCapital.charAt(i), beginCapitalLetter++);
+    }
+
+    for (int i = 0; i < encryptedMessage.length(); i++) {
+      if (Character.isAlphabetic(encryptedMessage.charAt(i)))
+        decoded.append(cipherMap.get(encryptedMessage.charAt(i)));
+      else decoded.append(encryptedMessage.charAt(i));
+    }
+
+    return decoded.toString();
+  }
+
+  /** TODO remove main and make JUnit Testing */
+  public static void main(String[] args) {
+    String a = encode("defend the east wall of the castle", "phqgiumeaylnofdxjkrcvstzwb");
+    String b = decode(a, "phqgiumeaylnofdxjkrcvstzwb");
+    System.out.println(b);
+  }
+}