Merge branch 'master' into abb_new_algo

Author: siriak

DIRECTORY.md

@@ -40,6 +40,13 @@
             <version>${assertj.version}</version>
             <scope>test</scope>
         </dependency>
+        <dependency>
+            <groupId>org.mockito</groupId>
+            <artifactId>mockito-core</artifactId>
+            <version>5.14.1</version>
+            <scope>test</scope>
+        </dependency>
+
 
         <dependency>
             <groupId>org.junit.jupiter</groupId>

pom.xml

@@ -87,9 +87,6 @@
         <Bug pattern="RCN_REDUNDANT_NULLCHECK_OF_NONNULL_VALUE" />
     </Match>
     <!-- fb-contrib -->
-    <Match>
-        <Bug pattern="OCP_OVERLY_CONCRETE_PARAMETER" />
-    </Match>
     <Match>
         <Bug pattern="LSC_LITERAL_STRING_COMPARISON" />
     </Match>

spotbugs-exclude.xml

@@ -4,32 +4,44 @@
 import java.util.List;
 
 /**
- * Finds all combinations of 0...n-1 of length k
+ * This class provides methods to find all combinations of integers from 0 to n-1
+ * of a specified length k using backtracking.
  */
 public final class ArrayCombination {
     private ArrayCombination() {
     }
 
     /**
-     * Finds all combinations of length k of 0..n-1 using backtracking.
+     * Generates all possible combinations of length k from the integers 0 to n-1.
      *
-     * @param n Number of the elements.
-     * @param k Length of the combination.
-     * @return A list of all combinations of length k.
+     * @param n The total number of elements (0 to n-1).
+     * @param k The desired length of each combination.
+     * @return A list containing all combinations of length k.
+     * @throws IllegalArgumentException if n or k are negative, or if k is greater than n.
      */
     public static List<List<Integer>> combination(int n, int k) {
         if (n < 0 || k < 0 || k > n) {
-            throw new IllegalArgumentException("Wrong input.");
+            throw new IllegalArgumentException("Invalid input: n must be non-negative, k must be non-negative and less than or equal to n.");
         }
 
         List<List<Integer>> combinations = new ArrayList<>();
         combine(combinations, new ArrayList<>(), 0, n, k);
         return combinations;
     }
 
+    /**
+     * A helper method that uses backtracking to find combinations.
+     *
+     * @param combinations The list to store all valid combinations found.
+     * @param current The current combination being built.
+     * @param start The starting index for the current recursion.
+     * @param n The total number of elements (0 to n-1).
+     * @param k The desired length of each combination.
+     */
     private static void combine(List<List<Integer>> combinations, List<Integer> current, int start, int n, int k) {
-        if (current.size() == k) { // Base case: combination found
-            combinations.add(new ArrayList<>(current)); // Copy to avoid modification
+        // Base case: combination found
+        if (current.size() == k) {
+            combinations.add(new ArrayList<>(current));
             return;
         }
 

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

@@ -1,6 +1,7 @@
 package com.thealgorithms.backtracking;
 
 import java.util.ArrayList;
+import java.util.Collection;
 import java.util.List;
 
 /**
@@ -95,7 +96,7 @@ public static void removeWord(char[][] puzzle, String word, int row, int col, bo
      * @param words  The list of words to be placed.
      * @return true if the crossword is solved, false otherwise.
      */
-    public static boolean solveCrossword(char[][] puzzle, List<String> words) {
+    public static boolean solveCrossword(char[][] puzzle, Collection<String> words) {
         // Create a mutable copy of the words list
         List<String> remainingWords = new ArrayList<>(words);
 

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

@@ -0,0 +1,147 @@
+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/main/java/com/thealgorithms/ciphers/RailFenceCipher.java

@@ -0,0 +1,23 @@
+package com.thealgorithms.conversions;
+
+/**
+ * Converts between big-endian and little-endian formats.
+ * Big-endian is the most significant byte first, while little-endian is the least significant byte first.
+ * Big-endian to little-endian: 0x12345678 -> 0x78563412
+ *
+ * Little-endian to big-endian: 0x12345678 -> 0x78563412
+ *
+ * @author Hardvan
+ */
+public final class EndianConverter {
+    private EndianConverter() {
+    }
+
+    public static int bigToLittleEndian(int value) {
+        return Integer.reverseBytes(value);
+    }
+
+    public static int littleToBigEndian(int value) {
+        return Integer.reverseBytes(value);
+    }
+}

src/main/java/com/thealgorithms/conversions/EndianConverter.java

@@ -0,0 +1,98 @@
+package com.thealgorithms.conversions;
+
+import java.util.HashMap;
+import java.util.Map;
+
+/**
+ * Converts text to Morse code and vice-versa.
+ * Text to Morse code: Each letter is separated by a space and each word is separated by a pipe (|).
+ * Example: "HELLO WORLD" -> ".... . .-.. .-.. --- | .-- --- .-. .-.. -.."
+ *
+ * Morse code to text: Each letter is separated by a space and each word is separated by a pipe (|).
+ * Example: ".... . .-.. .-.. --- | .-- --- .-. .-.. -.." -> "HELLO WORLD"
+ *
+ * Applications: Used in radio communications and algorithmic challenges.
+ *
+ * @author Hardvan
+ */
+public final class MorseCodeConverter {
+    private MorseCodeConverter() {
+    }
+
+    private static final Map<Character, String> MORSE_MAP = new HashMap<>();
+    private static final Map<String, Character> REVERSE_MAP = new HashMap<>();
+
+    static {
+        MORSE_MAP.put('A', ".-");
+        MORSE_MAP.put('B', "-...");
+        MORSE_MAP.put('C', "-.-.");
+        MORSE_MAP.put('D', "-..");
+        MORSE_MAP.put('E', ".");
+        MORSE_MAP.put('F', "..-.");
+        MORSE_MAP.put('G', "--.");
+        MORSE_MAP.put('H', "....");
+        MORSE_MAP.put('I', "..");
+        MORSE_MAP.put('J', ".---");
+        MORSE_MAP.put('K', "-.-");
+        MORSE_MAP.put('L', ".-..");
+        MORSE_MAP.put('M', "--");
+        MORSE_MAP.put('N', "-.");
+        MORSE_MAP.put('O', "---");
+        MORSE_MAP.put('P', ".--.");
+        MORSE_MAP.put('Q', "--.-");
+        MORSE_MAP.put('R', ".-.");
+        MORSE_MAP.put('S', "...");
+        MORSE_MAP.put('T', "-");
+        MORSE_MAP.put('U', "..-");
+        MORSE_MAP.put('V', "...-");
+        MORSE_MAP.put('W', ".--");
+        MORSE_MAP.put('X', "-..-");
+        MORSE_MAP.put('Y', "-.--");
+        MORSE_MAP.put('Z', "--..");
+
+        // Build reverse map for decoding
+        MORSE_MAP.forEach((k, v) -> REVERSE_MAP.put(v, k));
+    }
+
+    /**
+     * Converts text to Morse code.
+     * Each letter is separated by a space and each word is separated by a pipe (|).
+     *
+     * @param text The text to convert to Morse code.
+     * @return The Morse code representation of the text.
+     */
+    public static String textToMorse(String text) {
+        StringBuilder morse = new StringBuilder();
+        String[] words = text.toUpperCase().split(" ");
+        for (int i = 0; i < words.length; i++) {
+            for (char c : words[i].toCharArray()) {
+                morse.append(MORSE_MAP.getOrDefault(c, "")).append(" ");
+            }
+            if (i < words.length - 1) {
+                morse.append("| ");
+            }
+        }
+        return morse.toString().trim();
+    }
+
+    /**
+     * Converts Morse code to text.
+     * Each letter is separated by a space and each word is separated by a pipe (|).
+     *
+     * @param morse The Morse code to convert to text.
+     * @return The text representation of the Morse code.
+     */
+    public static String morseToText(String morse) {
+        StringBuilder text = new StringBuilder();
+        String[] words = morse.split(" \\| ");
+        for (int i = 0; i < words.length; i++) {
+            for (String code : words[i].split(" ")) {
+                text.append(REVERSE_MAP.getOrDefault(code, '?'));
+            }
+            if (i < words.length - 1) {
+                text.append(" ");
+            }
+        }
+        return text.toString();
+    }
+}