Add main, test for Rail Fence Cipher and update README.md

DIRECTORY.md

@@ -50,6 +50,7 @@
             * [AES](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/ciphers/AES.java)
             * [AESEncryption](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/ciphers/AESEncryption.java)
             * [AffineCipher](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/ciphers/AffineCipher.java)
+            * [AtbashCipher](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/ciphers/AtbashCipher.java)
             * [Autokey](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/ciphers/Autokey.java)
             * [Blowfish](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/ciphers/Blowfish.java)
             * [Caesar](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/ciphers/Caesar.java)
@@ -59,6 +60,7 @@
             * [PlayfairCipher](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/ciphers/PlayfairCipher.java)
             * [Polybius](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/ciphers/Polybius.java)
             * [ProductCipher](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/ciphers/ProductCipher.java)
+            * [RailFenceCipher](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/ciphers/RailFenceCipher.java)
             * [RSA](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/ciphers/RSA.java)
             * [SimpleSubCipher](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/ciphers/SimpleSubCipher.java)
             * [Vigenere](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/ciphers/Vigenere.java)
@@ -663,6 +665,7 @@
               * [LFSRTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/ciphers/a5/LFSRTest.java)
             * [AESEncryptionTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/ciphers/AESEncryptionTest.java)
             * [AffineCipherTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/ciphers/AffineCipherTest.java)
+            * [AtbashTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/ciphers/AtbashTest.java)
             * [AutokeyTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/ciphers/AutokeyTest.java)
             * [BlowfishTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/ciphers/BlowfishTest.java)
             * [CaesarTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/ciphers/CaesarTest.java)
@@ -671,6 +674,7 @@
             * [HillCipherTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/ciphers/HillCipherTest.java)
             * [PlayfairTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/ciphers/PlayfairTest.java)
             * [PolybiusTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/ciphers/PolybiusTest.java)
+            * [RailFenceTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/ciphers/RailFenceTest.java)
             * [RSATest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/ciphers/RSATest.java)
             * [SimpleSubCipherTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/ciphers/SimpleSubCipherTest.java)
             * [VigenereTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/ciphers/VigenereTest.java)

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

@@ -0,0 +1,71 @@
+package com.thealgorithms.ciphers;
+
+/**
+ * The Atbash cipher is a simple substitution cipher that replaces each letter
+ * in the alphabet with its reverse.
+ * For example, 'A' becomes 'Z', 'B' becomes 'Y', and so on. It works
+ * identically for both uppercase and lowercase letters.
+ * It's a symmetric cipher, meaning applying it twice returns the original text.
+ * Hence, the encrypting and the decrypting functions are identical
+ * @author https://github.com/Krounosity
+ * Learn more: https://en.wikipedia.org/wiki/Atbash
+ */
+
+public class AtbashCipher {
+
+    private String toConvert;
+
+    // Default constructor.
+    AtbashCipher() {
+    }
+
+    // String setting constructor.
+    AtbashCipher(String str) {
+        toConvert = str;
+    }
+
+    // String getter method.
+    public String getString() {
+        return toConvert;
+    }
+
+    // String setter method.
+    public void setString(String str) {
+        toConvert = str;
+    }
+
+    // Checking whether the current character is capital.
+    private boolean isCapital(char ch) {
+        return ch >= 'A' && ch <= 'Z';
+    }
+
+    // Checking whether the current character is smallcased.
+    private boolean isSmall(char ch) {
+        return ch >= 'a' && ch <= 'z';
+    }
+
+    // Converting text to atbash cipher code or vice versa.
+    public String convert() {
+
+        // Using StringBuilder to store new string.
+        StringBuilder convertedString = new StringBuilder();
+
+        // Iterating for each character.
+        for (char ch : toConvert.toCharArray()) {
+
+            // If the character is smallcased.
+            if (isSmall(ch)) {
+                convertedString.append((char) ('z' - (ch - 'a')));
+            }
+            // If the character is capital cased.
+            else if (isCapital(ch)) {
+                convertedString.append((char) ('Z' - (ch - 'A')));
+            }
+            // Non-alphabetical character.
+            else {
+                convertedString.append(ch);
+            }
+        }
+        return convertedString.toString();
+    }
+}

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

@@ -0,0 +1,129 @@
+package com.thealgorithms.ciphers;
+
+import java.util.Arrays;
+
+/**
+ * The rail fence cipher (also called a zigzag cipher) is a classical type of transposition cipher.
+ * It derives its name from the manner in which encryption is performed, in analogy to a fence built with horizontal rails.
+ * https://en.wikipedia.org/wiki/Rail_fence_cipher
+ * @author https://github.com/Krounosity
+ */
+
+
+ public class RailFenceCipher {
+
+    // Encrypts the input string using the rail fence cipher method with the given number of rails.
+    public String encrypt(String str, int rails) {
+
+        // Base case of single rail or rails are more than the number of characters in the string
+        if(rails == 1 || rails>=str.length()) return str;
+
+        // Boolean flag to determine if the movement is downward or upward in the rail matrix.
+        boolean down = true;
+        // Create a 2D array to represent the rails (rows) and the length of the string (columns).
+        char[][] strRail = new char[rails][str.length()];
+
+        // Initialize all positions in the rail matrix with a placeholder character ('\n').
+        for (int i = 0; i < rails; i++)
+            Arrays.fill(strRail[i], '\n');
+
+        int row = 0; // Start at the first row
+        int col = 0; // Start at the first column
+
+        int i = 0;
+
+        // Fill the rail matrix with characters from the string based on the rail pattern.
+        while (col < str.length()) {
+            // Change direction to down when at the first row.
+            if (row == 0) down = true;
+            // Change direction to up when at the last row.
+            else if (row == rails - 1) down = false;
+
+            // Place the character in the current position of the rail matrix.
+            strRail[row][col] = str.charAt(i);
+            col++; // Move to the next column.
+
+            // Move to the next row based on the direction.
+            if (down) row++;
+            else row--;
+
+            i++;
+        }
+
+        // Construct the encrypted string by reading characters row by row.
+        StringBuilder encryptedString = new StringBuilder();
+        for (char[] chRow : strRail) {
+            for (char ch : chRow) {
+                if (ch != '\n') encryptedString.append(ch);
+            }
+        }
+
+        return encryptedString.toString();
+    }
+
+    // Decrypts the input string using the rail fence cipher method with the given number of rails.
+    public String decrypt(String str, int rails) {
+
+        // Base case of single rail or rails are more than the number of characters in the string
+        if(rails == 1 || rails>=str.length()) return str;
+
+        // Boolean flag to determine if the movement is downward or upward in the rail matrix.
+        boolean down = true;
+
+        // Create a 2D array to represent the rails (rows) and the length of the string (columns).
+        char[][] strRail = new char[rails][str.length()];
+
+        int row = 0; // Start at the first row
+        int col = 0; // Start at the first column
+
+        // Mark the pattern on the rail matrix using '*'.
+        while (col < str.length()) {
+
+            // Change direction to down when at the first row.
+            if (row == 0) down = true;
+
+            // Change direction to up when at the last row.
+            else if (row == rails - 1) down = false;
+
+            // Mark the current position in the rail matrix.
+            strRail[row][col] = '*';
+            col++; // Move to the next column.
+
+            // Move to the next row based on the direction.
+            if (down) row++;
+            else row--;
+        }
+
+        int index = 0; // Index to track characters from the input string.
+        // Fill the rail matrix with characters from the input string based on the marked pattern.
+        for (int i = 0; i < rails; i++) {
+            for (int j = 0; j < str.length(); j++) {
+                if (strRail[i][j] == '*') {
+                    strRail[i][j] = str.charAt(index++);
+                }
+            }
+        }
+
+        // Construct the decrypted string by following the zigzag pattern.
+        StringBuilder decryptedString = new StringBuilder();
+        row = 0; // Reset to the first row
+        col = 0; // Reset to the first column
+
+        while (col < str.length()) {
+            // Change direction to down when at the first row.
+            if (row == 0) down = true;
+            // Change direction to up when at the last row.
+            else if (row == rails - 1) down = false;
+
+            // Append the character from the rail matrix to the decrypted string.
+            decryptedString.append(strRail[row][col]);
+            col++; // Move to the next column.
+
+            // Move to the next row based on the direction.
+            if (down) row++;
+            else row--;
+        }
+
+        return decryptedString.toString();
+    }
+}

src/test/java/com/thealgorithms/ciphers/AtbashTest.java

@@ -0,0 +1,28 @@
+package com.thealgorithms.ciphers;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import org.junit.jupiter.api.Test;
+
+public class AtbashTest {
+
+    @Test
+    public void atbashEncrypt() {
+        AtbashCipher normalToEncrypt = new AtbashCipher("Hello World! 123, @cipher abcDEF ZYX 987 madam zzZ Palindrome!");
+        String expectedText = "Svool Dliow! 123, @xrksvi zyxWVU ABC 987 nzwzn aaA Kzormwilnv!";
+
+        normalToEncrypt.setString(normalToEncrypt.convert());
+
+        assertEquals(expectedText, normalToEncrypt.getString());
+    }
+
+    @Test
+    public void atbashDecrypt() {
+        AtbashCipher encryptToNormal = new AtbashCipher("Svool Dliow! 123, @xrksvi zyxWVU ABC 987 nzwzn aaA Kzormwilnv!");
+        String expectedText = "Hello World! 123, @cipher abcDEF ZYX 987 madam zzZ Palindrome!";
+
+        encryptToNormal.setString(encryptToNormal.convert());
+
+        assertEquals(expectedText, encryptToNormal.getString());
+    }
+}

src/test/java/com/thealgorithms/ciphers/RailFenceTest.java

@@ -0,0 +1,62 @@
+package com.thealgorithms.ciphers;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import org.junit.jupiter.api.Test;
+
+public class RailFenceTest {
+
+    @Test
+    void testEncryption() {
+        RailFenceCipher cipher = new RailFenceCipher();
+
+        String input = "We are discovered! Flee at once";
+        int rails = 3;
+        String encrypted = cipher.encrypt(input, rails);
+        assertEquals("Wrivdlaneaedsoee!Fe toc  cr e e", encrypted);
+
+        String singleChar = "A";
+        int singleRail = 2;
+        String encryptedSingleChar = cipher.encrypt(singleChar, singleRail);
+        assertEquals("A", encryptedSingleChar);
+
+        String shortString = "Hello";
+        int moreRails = 10;
+        String encryptedShortString = cipher.encrypt(shortString, moreRails);
+        assertEquals("Hello", encryptedShortString);
+
+        String inputSingleRail = "Single line";
+        int singleRailOnly = 1;
+        String encryptedSingleRail = cipher.encrypt(inputSingleRail, singleRailOnly);
+        assertEquals("Single line", encryptedSingleRail);
+    }
+
+    @Test
+    void testDecryption() {
+        RailFenceCipher cipher = new RailFenceCipher();
+
+        // Scenario 1: Basic decryption with multiple rails
+        String encryptedInput = "Wrivdlaneaedsoee!Fe toc  cr e e";
+        int rails = 3;
+        String decrypted = cipher.decrypt(encryptedInput, rails);
+        assertEquals("We are discovered! Flee at once", decrypted);
+
+        // Scenario 2: Single character string decryption
+        String encryptedSingleChar = "A";
+        int singleRail = 2; // More than 1 rail
+        String decryptedSingleChar = cipher.decrypt(encryptedSingleChar, singleRail);
+        assertEquals("A", decryptedSingleChar);
+
+        // Scenario 3: String length less than the number of rails
+        String encryptedShortString = "Hello";
+        int moreRails = 10; // More rails than characters
+        String decryptedShortString = cipher.decrypt(encryptedShortString, moreRails);
+        assertEquals("Hello", decryptedShortString);
+
+        // Scenario 4: Single rail decryption (output should be the same as input)
+        String encryptedSingleRail = "Single line";
+        int singleRailOnly = 1;
+        String decryptedSingleRail = cipher.decrypt(encryptedSingleRail, singleRailOnly);
+        assertEquals("Single line", decryptedSingleRail);
+    }
+}