Merge remote-tracking branch 'origin/median_sorted_arrays_new_algo' into median_sorted_arrays_new_algo

Author: Hardvan

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

@@ -1,51 +1,72 @@
 package com.thealgorithms.backtracking;
 
-/*
-Word Search Problem (https://en.wikipedia.org/wiki/Word_search)
-
-Given an m x n grid of characters board and a string word, return true if word exists in the grid.
-
-The word can be constructed from letters of sequentially adjacent cell, where "adjacent" cells are
-those horizontally or vertically neighboring. The same letter cell may not be used more than once.
-
-For example,
-Given board =
-
-[
- ['A','B','C','E'],
- ['S','F','C','S'],
- ['A','D','E','E']
-]
-word = "ABCCED", -> returns true,
-word = "SEE", -> returns true,
-word = "ABCB", -> returns false.
-*/
-
-/*
-   Solution
-   Depth First Search in matrix (as multiple sources possible) with backtracking
-   like finding cycle in a directed graph. Maintain a record of path
-
-   Tx = O(m * n * 3^L): for each cell, we look at 3 options (not 4 as that one will be visited), we
-   do it L times Sx = O(L) : stack size is max L
-*/
-
+/**
+ * Word Search Problem
+ *
+ * This class solves the word search problem where given an m x n grid of characters (board)
+ * and a target word, the task is to check if the word exists in the grid.
+ * The word can be constructed from sequentially adjacent cells (horizontally or vertically),
+ * and the same cell may not be used more than once in constructing the word.
+ *
+ * Example:
+ * - For board =
+ *     [
+ *       ['A','B','C','E'],
+ *       ['S','F','C','S'],
+ *       ['A','D','E','E']
+ *     ]
+ *   and word = "ABCCED", -> returns true
+ *   and word = "SEE",    -> returns true
+ *   and word = "ABCB",   -> returns false
+ *
+ * Solution:
+ * - Depth First Search (DFS) with backtracking is used to explore possible paths from any cell
+ *   matching the first letter of the word. DFS ensures that we search all valid paths, while
+ *   backtracking helps in reverting decisions when a path fails to lead to a solution.
+ *
+ * Time Complexity: O(m * n * 3^L)
+ *  - m = number of rows in the board
+ *  - n = number of columns in the board
+ *  - L = length of the word
+ *  - For each cell, we look at 3 possible directions (since we exclude the previously visited direction),
+ *    and we do this for L letters.
+ *
+ * Space Complexity: O(L)
+ *  - Stack space for the recursive DFS function, where L is the maximum depth of recursion (length of the word).
+ */
 public class WordSearch {
     private final int[] dx = {0, 0, 1, -1};
     private final int[] dy = {1, -1, 0, 0};
     private boolean[][] visited;
     private char[][] board;
     private String word;
 
+    /**
+     * Checks if the given (x, y) coordinates are valid positions in the board.
+     *
+     * @param x The row index.
+     * @param y The column index.
+     * @return True if the coordinates are within the bounds of the board; false otherwise.
+     */
     private boolean isValid(int x, int y) {
         return x >= 0 && x < board.length && y >= 0 && y < board[0].length;
     }
 
+    /**
+     * Performs Depth First Search (DFS) from the cell (x, y)
+     * to search for the next character in the word.
+     *
+     * @param x       The current row index.
+     * @param y       The current column index.
+     * @param nextIdx The index of the next character in the word to be matched.
+     * @return True if a valid path is found to match the remaining characters of the word; false otherwise.
+     */
     private boolean doDFS(int x, int y, int nextIdx) {
         visited[x][y] = true;
         if (nextIdx == word.length()) {
             return true;
         }
+
         for (int i = 0; i < 4; ++i) {
             int xi = x + dx[i];
             int yi = y + dy[i];
@@ -56,10 +77,19 @@ private boolean doDFS(int x, int y, int nextIdx) {
                 }
             }
         }
-        visited[x][y] = false;
+
+        visited[x][y] = false; // Backtrack
         return false;
     }
 
+    /**
+     * Main function to check if the word exists in the board. It initiates DFS from any
+     * cell that matches the first character of the word.
+     *
+     * @param board The 2D grid of characters (the board).
+     * @param word  The target word to search for in the board.
+     * @return True if the word exists in the board; false otherwise.
+     */
     public boolean exist(char[][] board, String word) {
         this.board = board;
         this.word = word;

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

@@ -1,17 +1,39 @@
 package com.thealgorithms.bitmanipulation;
+
 import java.util.Optional;
 
 /**
  * Find Highest Set Bit
- * This class provides a function calculating the position (or index)
- * of the most significant bit being set to 1 in a given integer.
- * @author Bama Charan Chhandogi (https://github.com/BamaCharanChhandogi)
+ *
+ * This class provides a utility method to calculate the position of the highest
+ * (most significant) bit that is set to 1 in a given non-negative integer.
+ * It is often used in bit manipulation tasks to find the left-most set bit in binary
+ * representation of a number.
+ *
+ * Example:
+ * - For input 18 (binary 10010), the highest set bit is at position 4 (zero-based index).
+ *
+ * @author Bama Charan Chhandogi
+ * @version 1.0
+ * @since 2021-06-23
  */
-
 public final class HighestSetBit {
+
     private HighestSetBit() {
     }
 
+    /**
+     * Finds the highest (most significant) set bit in the given integer.
+     * The method returns the position (index) of the highest set bit as an {@link Optional}.
+     *
+     * - If the number is 0, no bits are set, and the method returns {@link Optional#empty()}.
+     * - If the number is negative, the method throws {@link IllegalArgumentException}.
+     *
+     * @param num The input integer for which the highest set bit is to be found. It must be non-negative.
+     * @return An {@link Optional} containing the index of the highest set bit (zero-based).
+     *         Returns {@link Optional#empty()} if the number is 0.
+     * @throws IllegalArgumentException if the input number is negative.
+     */
     public static Optional<Integer> findHighestSetBit(int num) {
         if (num < 0) {
             throw new IllegalArgumentException("Input cannot be negative");
@@ -27,6 +49,6 @@ public static Optional<Integer> findHighestSetBit(int num) {
             position++;
         }
 
-        return Optional.of(position - 1);
+        return Optional.of(position - 1); // Subtract 1 to convert to zero-based index
     }
 }

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

@@ -1,13 +1,27 @@
 package com.thealgorithms.bitmanipulation;
 
 /**
- * Find The Index Of Right Most SetBit
- * @author Bama Charan Chhandogi (https://github.com/BamaCharanChhandogi)
+ * Utility class for bit manipulation operations.
+ * This class provides methods to work with bitwise operations.
+ * Specifically, it includes a method to find the index of the rightmost set bit
+ * in an integer.
+ * This class is not meant to be instantiated.
+ *
+ * Author: Bama Charan Chhandogi (https://github.com/BamaCharanChhandogi)
  */
-
 public final class IndexOfRightMostSetBit {
+
     private IndexOfRightMostSetBit() {
     }
+
+    /**
+     * Finds the index of the rightmost set bit in the given integer.
+     * The index is zero-based, meaning the rightmost bit has an index of 0.
+     *
+     * @param n the integer to check for the rightmost set bit
+     * @return the index of the rightmost set bit; -1 if there are no set bits
+     *         (i.e., the input integer is 0)
+     */
     public static int indexOfRightMostSetBit(int n) {
         if (n == 0) {
             return -1; // No set bits
@@ -16,7 +30,7 @@ public static int indexOfRightMostSetBit(int n) {
         // Handle negative numbers by finding the two's complement
         if (n < 0) {
             n = -n;
-            n = n & (~n + 1); // Get the rightmost set bit in positive form
+            n = n & (~n + 1); // Isolate the rightmost set bit
         }
 
         int index = 0;

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

@@ -0,0 +1,34 @@
+package com.thealgorithms.bitmanipulation;
+
+/**
+ * Lowest Set Bit
+ * @author Prayas Kumar (https://github.com/prayas7102)
+ */
+
+public final class LowestSetBit {
+    // Private constructor to hide the default public one
+    private LowestSetBit() {
+    }
+    /**
+     * Isolates the lowest set bit of the given number. For example, if n = 18
+     * (binary: 10010), the result will be 2 (binary: 00010).
+     *
+     * @param n the number whose lowest set bit will be isolated
+     * @return the isolated lowest set bit of n
+     */
+    public static int isolateLowestSetBit(int n) {
+        // Isolate the lowest set bit using n & -n
+        return n & -n;
+    }
+    /**
+     * Clears the lowest set bit of the given number.
+     * For example, if n = 18 (binary: 10010), the result will be 16 (binary: 10000).
+     *
+     * @param n the number whose lowest set bit will be cleared
+     * @return the number after clearing its lowest set bit
+     */
+    public static int clearLowestSetBit(int n) {
+        // Clear the lowest set bit using n & (n - 1)
+        return n & (n - 1);
+    }
+}