Merge branch 'master' into Feature-ShuffleArray

Author: siriak

DIRECTORY.md

@@ -114,7 +114,7 @@
             <plugin>
                 <groupId>org.apache.maven.plugins</groupId>
                 <artifactId>maven-checkstyle-plugin</artifactId>
-                <version>3.5.0</version>
+                <version>3.6.0</version>
                 <configuration>
                     <configLocation>checkstyle.xml</configLocation>
                     <consoleOutput>true</consoleOutput>
@@ -125,7 +125,7 @@
                     <dependency>
                     <groupId>com.puppycrawl.tools</groupId>
                     <artifactId>checkstyle</artifactId>
-                    <version>10.18.2</version>
+                    <version>10.19.0</version>
                     </dependency>
                 </dependencies>
             </plugin>
@@ -153,7 +153,7 @@
             <plugin>
                 <groupId>org.apache.maven.plugins</groupId>
                 <artifactId>maven-pmd-plugin</artifactId>
-                <version>3.25.0</version>
+                <version>3.26.0</version>
                 <configuration>
                     <printFailingErrors>true</printFailingErrors>
                     <includeTests>true</includeTests>

pom.xml

@@ -1,6 +1,7 @@
 package com.thealgorithms.backtracking;
 
 import java.util.Arrays;
+import java.util.Collections;
 import java.util.LinkedList;
 import java.util.List;
 import java.util.TreeSet;
@@ -13,8 +14,6 @@ public final class Combination {
     private Combination() {
     }
 
-    private static int length;
-
     /**
      * Find all combinations of given array using backtracking
      * @param arr the array.
@@ -23,39 +22,45 @@ private Combination() {
      * @return a list of all combinations of length n. If n == 0, return null.
      */
     public static <T> List<TreeSet<T>> combination(T[] arr, int n) {
+        if (n < 0) {
+            throw new IllegalArgumentException("The combination length cannot be negative.");
+        }
+
         if (n == 0) {
-            return null;
+            return Collections.emptyList();
         }
-        length = n;
         T[] array = arr.clone();
         Arrays.sort(array);
+
         List<TreeSet<T>> result = new LinkedList<>();
-        backtracking(array, 0, new TreeSet<T>(), result);
+        backtracking(array, n, 0, new TreeSet<T>(), result);
         return result;
     }
 
     /**
      * Backtrack all possible combinations of a given array
      * @param arr the array.
+     * @param n length of the combination
      * @param index the starting index.
      * @param currSet set that tracks current combination
      * @param result the list contains all combination.
      * @param <T> the type of elements in the array.
      */
-    private static <T> void backtracking(T[] arr, int index, TreeSet<T> currSet, List<TreeSet<T>> result) {
-        if (index + length - currSet.size() > arr.length) {
+    private static <T> void backtracking(T[] arr, int n, int index, TreeSet<T> currSet, List<TreeSet<T>> result) {
+        if (index + n - currSet.size() > arr.length) {
             return;
         }
-        if (length - 1 == currSet.size()) {
+        if (currSet.size() == n - 1) {
             for (int i = index; i < arr.length; i++) {
                 currSet.add(arr[i]);
-                result.add((TreeSet<T>) currSet.clone());
+                result.add(new TreeSet<>(currSet));
                 currSet.remove(arr[i]);
             }
+            return;
         }
         for (int i = index; i < arr.length; i++) {
             currSet.add(arr[i]);
-            backtracking(arr, i + 1, currSet, result);
+            backtracking(arr, n, i + 1, currSet, result);
             currSet.remove(arr[i]);
         }
     }

src/main/java/com/thealgorithms/backtracking/Combination.java

@@ -0,0 +1,44 @@
+package com.thealgorithms.bitmanipulation;
+
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * This class provides a method to generate all subsets (power set)
+ * of a given set using bit manipulation.
+ *
+ * @author Hardvan
+ */
+public final class GenerateSubsets {
+    private GenerateSubsets() {
+    }
+
+    /**
+     * Generates all subsets of a given set using bit manipulation.
+     * Steps:
+     * 1. Iterate over all numbers from 0 to 2^n - 1.
+     * 2. For each number, iterate over all bits from 0 to n - 1.
+     * 3. If the i-th bit of the number is set, add the i-th element of the set to the current subset.
+     * 4. Add the current subset to the list of subsets.
+     * 5. Return the list of subsets.
+     *
+     * @param set the input set of integers
+     * @return a list of all subsets represented as lists of integers
+     */
+    public static List<List<Integer>> generateSubsets(int[] set) {
+        int n = set.length;
+        List<List<Integer>> subsets = new ArrayList<>();
+
+        for (int mask = 0; mask < (1 << n); mask++) {
+            List<Integer> subset = new ArrayList<>();
+            for (int i = 0; i < n; i++) {
+                if ((mask & (1 << i)) != 0) {
+                    subset.add(set[i]);
+                }
+            }
+            subsets.add(subset);
+        }
+
+        return subsets;
+    }
+}

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

@@ -0,0 +1,30 @@
+package com.thealgorithms.bitmanipulation;
+
+/**
+ * This class provides a method to find the next higher number
+ * with the same number of set bits as the given number.
+ *
+ * @author Hardvan
+ */
+public final class NextHigherSameBitCount {
+    private NextHigherSameBitCount() {
+    }
+
+    /**
+     * Finds the next higher integer with the same number of set bits.
+     * Steps:
+     * 1. Find {@code c}, the rightmost set bit of {@code n}.
+     * 2. Find {@code r}, the rightmost set bit of {@code n + c}.
+     * 3. Swap the bits of {@code r} and {@code n} to the right of {@code c}.
+     * 4. Shift the bits of {@code r} and {@code n} to the right of {@code c} to the rightmost.
+     * 5. Combine the results of steps 3 and 4.
+     *
+     * @param n the input number
+     * @return the next higher integer with the same set bit count
+     */
+    public static int nextHigherSameBitCount(int n) {
+        int c = n & -n;
+        int r = n + c;
+        return (((r ^ n) >> 2) / c) | r;
+    }
+}

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

@@ -1,14 +1,33 @@
 package com.thealgorithms.bitmanipulation;
 
 /**
- * Converts any Octal Number to a Binary Number
+ * This class provides a method to reverse the bits of a 32-bit integer.
+ * Reversing the bits means that the least significant bit (LSB) becomes
+ * the most significant bit (MSB) and vice versa.
+ *
+ * Example:
+ * Input (binary): 00000010100101000001111010011100 (43261596)
+ * Output (binary): 00111001011110000010100101000000 (964176192)
+ *
+ * Time Complexity: O(32) - A fixed number of 32 iterations
+ * Space Complexity: O(1) - No extra space used
+ *
+ * Note:
+ * - If the input is negative, Java handles it using two’s complement representation.
+ * - This function works on 32-bit integers by default.
+ *
  * @author Bama Charan Chhandogi
  */
-
 public final class ReverseBits {
     private ReverseBits() {
     }
 
+    /**
+     * Reverses the bits of a 32-bit integer.
+     *
+     * @param n the integer whose bits are to be reversed
+     * @return the integer obtained by reversing the bits of the input
+     */
     public static int reverseBits(int n) {
         int result = 0;
         int bitCount = 32;

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

@@ -1,14 +1,45 @@
 package com.thealgorithms.bitmanipulation;
 
 /**
- * Swap every pair of adjacent bits of a given number.
- * @author Lakshyajeet Singh Goyal (https://github.com/DarkMatter-999)
+ * A utility class to swap every pair of adjacent bits in a given integer.
+ * This operation shifts the even-positioned bits to odd positions and vice versa.
+ *
+ * Example:
+ * - Input: 2 (binary: `10`) → Output: 1 (binary: `01`)
+ * - Input: 43 (binary: `101011`) → Output: 23 (binary: `010111`)
+ *
+ * **Explanation of the Algorithm:**
+ * 1. Mask even-positioned bits: Using `0xAAAAAAAA` (binary: `101010...`),
+ *    which selects bits in even positions.
+ * 2. Mask odd-positioned bits: Using `0x55555555` (binary: `010101...`),
+ *    which selects bits in odd positions.
+ * 3. Shift bits:
+ *    - Right-shift even-positioned bits by 1 to move them to odd positions.
+ *    - Left-shift odd-positioned bits by 1 to move them to even positions.
+ * 4. Combine both shifted results using bitwise OR (`|`) to produce the final result.
+ *
+ * Use Case: This algorithm can be useful in applications involving low-level bit manipulation,
+ * such as encoding, data compression, or cryptographic transformations.
+ *
+ * Time Complexity: O(1) (constant time, since operations are bitwise).
+ *
+ * Author: Lakshyajeet Singh Goyal (https://github.com/DarkMatter-999)
  */
-
 public final class SwapAdjacentBits {
     private SwapAdjacentBits() {
     }
 
+    /**
+     * Swaps every pair of adjacent bits of a given integer.
+     * Steps:
+     * 1. Mask the even-positioned bits.
+     * 2. Mask the odd-positioned bits.
+     * 3. Shift the even bits to the right and the odd bits to the left.
+     * 4. Combine the shifted bits.
+     *
+     * @param num the integer whose bits are to be swapped
+     * @return the integer after swapping every pair of adjacent bits
+     */
     public static int swapAdjacentBits(int num) {
         // mask the even bits (0xAAAAAAAA => 10101010...)
         int evenBits = num & 0xAAAAAAAA;