Merge branch 'master' into lfu_cache_improvement

Author: alxkm

DIRECTORY.md

@@ -20,7 +20,7 @@
             <dependency>
                 <groupId>org.junit</groupId>
                 <artifactId>junit-bom</artifactId>
-                <version>5.11.1</version>
+                <version>5.11.2</version>
                 <type>pom</type>
                 <scope>import</scope>
             </dependency>
@@ -31,7 +31,7 @@
         <dependency>
             <groupId>org.junit.jupiter</groupId>
             <artifactId>junit-jupiter</artifactId>
-            <version>5.11.1</version>
+            <version>5.11.2</version>
             <scope>test</scope>
         </dependency>
         <dependency>
@@ -44,7 +44,7 @@
         <dependency>
             <groupId>org.junit.jupiter</groupId>
             <artifactId>junit-jupiter-api</artifactId>
-            <version>5.11.1</version>
+            <version>5.11.2</version>
             <scope>test</scope>
         </dependency>
         <dependency>

pom.xml

@@ -0,0 +1,36 @@
+package com.thealgorithms.Recursion;
+
+// program to find power set of a string
+
+import java.util.ArrayList;
+import java.util.List;
+
+public final class GenerateSubsets {
+
+    private GenerateSubsets() {
+        throw new UnsupportedOperationException("Utility class");
+    }
+
+    public static List<String> subsetRecursion(String str) {
+        return doRecursion("", str);
+    }
+
+    private static List<String> doRecursion(String p, String up) {
+        if (up.isEmpty()) {
+            List<String> list = new ArrayList<>();
+            list.add(p);
+            return list;
+        }
+
+        // Taking the character
+        char ch = up.charAt(0);
+        // Adding the character in the recursion
+        List<String> left = doRecursion(p + ch, up.substring(1));
+        // Not adding the character in the recursion
+        List<String> right = doRecursion(p, up.substring(1));
+
+        left.addAll(right);
+
+        return left;
+    }
+}

src/main/java/com/thealgorithms/Recursion/GenerateSubsets.java

@@ -1,4 +1,4 @@
-package com.thealgorithms.others;
+package com.thealgorithms.bitmanipulation;
 
 public class CountSetBits {
 
@@ -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/others/CountSetBits.java renamed to src/main/java/com/thealgorithms/bitmanipulation/CountSetBits.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();
+    }
+}