Merge branch 'master' into hrr_new_algo

Author: Hardvan

DIRECTORY.md

@@ -42,6 +42,7 @@
             * [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)
+            * [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)
             * [ColumnarTranspositionCipher](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/ciphers/ColumnarTranspositionCipher.java)
@@ -203,6 +204,7 @@
               * [SameTreesCheck](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/datastructures/trees/SameTreesCheck.java)
               * [SegmentTree](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/datastructures/trees/SegmentTree.java)
               * [SplayTree](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/datastructures/trees/SplayTree.java)
+              * [Treap](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/datastructures/trees/Treap.java)
               * [TreeRandomNode](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/datastructures/trees/TreeRandomNode.java)
               * [TrieImp](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/datastructures/trees/TrieImp.java)
               * [VerticalOrderTraversal](https://github.com/TheAlgorithms/Java/blob/master/src/main/java/com/thealgorithms/datastructures/trees/VerticalOrderTraversal.java)
@@ -619,6 +621,7 @@
           * ciphers
             * a5
               * [LFSRTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/ciphers/a5/LFSRTest.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)
             * [DESTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/ciphers/DESTest.java)
@@ -729,6 +732,7 @@
               * [PreOrderTraversalTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/trees/PreOrderTraversalTest.java)
               * [SameTreesCheckTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/trees/SameTreesCheckTest.java)
               * [SplayTreeTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/trees/SplayTreeTest.java)
+              * [TreapTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/trees/TreapTest.java)
               * [TreeTestUtils](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/trees/TreeTestUtils.java)
               * [TrieImpTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/trees/TrieImpTest.java)
               * [VerticalOrderTraversalTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/datastructures/trees/VerticalOrderTraversalTest.java)

src/main/java/com/thealgorithms/bitmanipulation/CountSetBits.java

@@ -48,4 +48,32 @@ public long countSetBits(long num) {
         }
         return cnt;
     }
+
+    /**
+     * This approach takes O(1) running time to count the set bits, but requires a pre-processing.
+     *
+     * So, we divide our 32-bit input into 8-bit chunks, with four chunks. We have 8 bits in each chunk.
+     *
+     * Then the range is from 0-255 (0 to 2^7).
+     * So, we may need to count set bits from 0 to 255 in individual chunks.
+     *
+     * @param num takes a long number
+     * @return the count of set bits in the binary equivalent
+     */
+    public int lookupApproach(int num) {
+        int[] table = new int[256];
+        table[0] = 0;
+
+        for (int i = 1; i < 256; i++) {
+            table[i] = (i & 1) + table[i >> 1]; // i >> 1 equals to i/2
+        }
+
+        int res = 0;
+        for (int i = 0; i < 4; i++) {
+            res += table[num & 0xff];
+            num >>= 8;
+        }
+
+        return res;
+    }
 }

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

@@ -0,0 +1,55 @@
+package com.thealgorithms.ciphers;
+
+/**
+ * The Autokey Cipher is an interesting and historically significant encryption method,
+ * as it improves upon the classic Vigenère Cipher by using the plaintext itself to
+ * extend the key. This makes it harder to break using frequency analysis, as it
+ * doesn’t rely solely on a repeated key.
+ * https://en.wikipedia.org/wiki/Autokey_cipher
+ *
+ * @author bennybebo
+ */
+public class Autokey {
+
+    // Encrypts the plaintext using the Autokey cipher
+    public String encrypt(String plaintext, String keyword) {
+        plaintext = plaintext.toUpperCase().replaceAll("[^A-Z]", ""); // Sanitize input
+        keyword = keyword.toUpperCase();
+
+        StringBuilder extendedKey = new StringBuilder(keyword);
+        extendedKey.append(plaintext); // Extend key with plaintext
+
+        StringBuilder ciphertext = new StringBuilder();
+
+        for (int i = 0; i < plaintext.length(); i++) {
+            char plainChar = plaintext.charAt(i);
+            char keyChar = extendedKey.charAt(i);
+
+            int encryptedChar = (plainChar - 'A' + keyChar - 'A') % 26 + 'A';
+            ciphertext.append((char) encryptedChar);
+        }
+
+        return ciphertext.toString();
+    }
+
+    // Decrypts the ciphertext using the Autokey cipher
+    public String decrypt(String ciphertext, String keyword) {
+        ciphertext = ciphertext.toUpperCase().replaceAll("[^A-Z]", ""); // Sanitize input
+        keyword = keyword.toUpperCase();
+
+        StringBuilder plaintext = new StringBuilder();
+        StringBuilder extendedKey = new StringBuilder(keyword);
+
+        for (int i = 0; i < ciphertext.length(); i++) {
+            char cipherChar = ciphertext.charAt(i);
+            char keyChar = extendedKey.charAt(i);
+
+            int decryptedChar = (cipherChar - 'A' - (keyChar - 'A') + 26) % 26 + 'A';
+            plaintext.append((char) decryptedChar);
+
+            extendedKey.append((char) decryptedChar); // Extend key with each decrypted char
+        }
+
+        return plaintext.toString();
+    }
+}