feat: Added VerhoeffSnippet class to Algorithm package (#239)

* Added VerhoeffSnippet class to Algorithm package

Added VerhoeffSnippet  class

Added VerhoeffSnippetTest class

Added VerhoeffSnippet class to README.md

* checkstyle indentation fixed

README.md

@@ -435,6 +435,76 @@ public class SieveOfEratosthenesSnippet {
   }
 }
 ```
+### Verhoeff
+
+```java
+public class VerhoeffSnippet {
+
+    private static final int[][] d = {
+            {0, 1, 2, 3, 4, 5, 6, 7, 8, 9},
+            {1, 0, 3, 2, 5, 4, 7, 6, 9, 8},
+            {2, 3, 0, 1, 6, 7, 4, 5, 8, 9},
+            {3, 2, 1, 0, 7, 6, 5, 4, 9, 8},
+            {4, 5, 6, 7, 0, 1, 2, 3, 8, 9},
+            {5, 4, 7, 6, 1, 0, 3, 2, 9, 8},
+            {6, 7, 4, 5, 2, 3, 0, 1, 8, 9},
+            {7, 6, 5, 4, 3, 2, 1, 0, 9, 8},
+            {8, 9, 8, 9, 8, 9, 8, 9, 0, 1},
+            {9, 8, 9, 8, 9, 8, 9, 8, 1, 0}
+    };
+
+    private static final int[][] p = {
+            {0, 1, 2, 3, 4, 5, 6, 7, 8, 9},
+            {1, 5, 7, 6, 2, 8, 3, 0, 9, 4},
+            {5, 8, 0, 3, 7, 9, 6, 1, 4, 2},
+            {8, 9, 1, 6, 0, 4, 3, 5, 2, 7},
+            {9, 4, 5, 3, 1, 2, 6, 8, 7, 0},
+            {4, 2, 8, 6, 5, 7, 3, 9, 0, 1},
+            {2, 7, 9, 3, 8, 0, 6, 4, 1, 5},
+            {7, 0, 4, 6, 9, 1, 3, 2, 5, 8}
+    };
+
+    private static final int[] inv = {0, 4, 3, 2, 1, 5, 6, 7, 8, 9};
+
+    /**
+     * Validates a number using the Verhoeff checksum algorithm.
+     *
+     * @param num the numeric string to validate
+     * @return true if the number is valid according to Verhoeff algorithm, false otherwise
+     */
+    public static boolean validateVerhoeff(String num) {
+        int c = 0;
+        int length = num.length();
+
+        // Adjust index for validation of the full number (including check digit)
+        for (int i = 0; i < length; i++) {
+            int digit = Character.getNumericValue(num.charAt(length - i - 1));
+            c = d[c][p[(i + 1) % 8][digit]]; // Correct permutation index
+        }
+
+        return c == 0; // Final checksum must be zero
+    }
+
+    /**
+     * Generates a Verhoeff check digit for a given numeric string.
+     *
+     * @param num the numeric string for which to generate the check digit
+     * @return the generated Verhoeff check digit as a string
+     */
+    public static String generateVerhoeff(String num) {
+        int c = 0;
+        int length = num.length();
+
+        for (int i = 0; i < length; i++) {
+            int digit = Character.getNumericValue(num.charAt(length - i - 1));
+            c = d[c][p[(i % 8)][digit]];
+        }
+
+        return Integer.toString(inv[c]);
+    }
+
+}
+```
 
 ## Array
 

src/main/java/algorithm/VerhoeffSnippet.java

@@ -0,0 +1,95 @@
+/*
+ * MIT License
+ *
+ * Copyright (c) 2017-2022 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+package algorithm;
+
+/**
+ * VerhoeffSnippet.
+ */
+public class VerhoeffSnippet {
+
+  private static final int[][] d = {
+          {0, 1, 2, 3, 4, 5, 6, 7, 8, 9},
+          {1, 0, 3, 2, 5, 4, 7, 6, 9, 8},
+          {2, 3, 0, 1, 6, 7, 4, 5, 8, 9},
+          {3, 2, 1, 0, 7, 6, 5, 4, 9, 8},
+          {4, 5, 6, 7, 0, 1, 2, 3, 8, 9},
+          {5, 4, 7, 6, 1, 0, 3, 2, 9, 8},
+          {6, 7, 4, 5, 2, 3, 0, 1, 8, 9},
+          {7, 6, 5, 4, 3, 2, 1, 0, 9, 8},
+          {8, 9, 8, 9, 8, 9, 8, 9, 0, 1},
+          {9, 8, 9, 8, 9, 8, 9, 8, 1, 0}
+  };
+
+  private static final int[][] p = {
+          {0, 1, 2, 3, 4, 5, 6, 7, 8, 9},
+          {1, 5, 7, 6, 2, 8, 3, 0, 9, 4},
+          {5, 8, 0, 3, 7, 9, 6, 1, 4, 2},
+          {8, 9, 1, 6, 0, 4, 3, 5, 2, 7},
+          {9, 4, 5, 3, 1, 2, 6, 8, 7, 0},
+          {4, 2, 8, 6, 5, 7, 3, 9, 0, 1},
+          {2, 7, 9, 3, 8, 0, 6, 4, 1, 5},
+          {7, 0, 4, 6, 9, 1, 3, 2, 5, 8}
+  };
+
+  private static final int[] inv = {0, 4, 3, 2, 1, 5, 6, 7, 8, 9};
+
+  /**
+   * Validates a number using the Verhoeff checksum algorithm.
+   *
+   * @param num the numeric string to validate
+   * @return true if the number is valid according to Verhoeff algorithm, false otherwise
+   */
+  public static boolean validateVerhoeff(String num) {
+    int c = 0;
+    int length = num.length();
+
+    // Adjust index for validation of the full number (including check digit)
+    for (int i = 0; i < length; i++) {
+      int digit = Character.getNumericValue(num.charAt(length - i - 1));
+      c = d[c][p[(i + 1) % 8][digit]]; // Correct permutation index
+    }
+
+    return c == 0; // Final checksum must be zero
+  }
+
+  /**
+   * Generates a Verhoeff check digit for a given numeric string.
+   *
+   * @param num the numeric string for which to generate the check digit
+   * @return the generated Verhoeff check digit as a string
+   */
+  public static String generateVerhoeff(String num) {
+    int c = 0;
+    int length = num.length();
+
+    for (int i = 0; i < length; i++) {
+      int digit = Character.getNumericValue(num.charAt(length - i - 1));
+      c = d[c][p[(i % 8)][digit]];
+    }
+
+    return Integer.toString(inv[c]);
+  }
+
+}

src/test/java/algorithm/VerhoeffSnippetTest.java

@@ -0,0 +1,78 @@
+/*
+ * MIT License
+ *
+ * Copyright (c) 2017-2022 Ilkka Seppälä
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+package algorithm;
+
+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import org.junit.jupiter.api.Test;
+
+/**
+ * Tests for VerhoeffSnippet.
+ */
+class VerhoeffSnippetTest {
+
+  /**
+   * Tests the {@link VerhoeffSnippet#validateVerhoeff(String)} method.
+   */
+  @Test
+  void testValidateVerhoeff() {
+    String validInput = "1428579";   // Correct Verhoeff input with a valid check digit
+    String invalidInput = "1428570"; // Incorrect Verhoeff input with an invalid check digit
+
+    // Validate valid input
+    boolean isValid = VerhoeffSnippet.validateVerhoeff(validInput);
+    System.out.println("Testing validateVerhoeff with valid input: "
+            + validInput + " -> " + isValid);
+    assertTrue(isValid, "Expected " + validInput + " to be valid, but it was not.");
+
+    // Validate invalid input
+    boolean isInvalid = VerhoeffSnippet.validateVerhoeff(invalidInput);
+    System.out.println("Testing validateVerhoeff with invalid input: "
+            + invalidInput + " -> " + isInvalid);
+    assertFalse(isInvalid, "Expected " + invalidInput + " to be invalid, but it was not.");
+  }
+
+  /**
+   * Tests the {@link VerhoeffSnippet#generateVerhoeff(String)} method.
+   */
+  @Test
+  void testGenerateVerhoeff() {
+    String baseInput = "142857"; // Base input without the Verhoeff check digit
+
+    // Generate a Verhoeff check digit
+    String checkDigit = VerhoeffSnippet.generateVerhoeff(baseInput);
+    assertTrue("9".equals(checkDigit),
+            "Expected check digit to be 9 for input " + baseInput + ", but got " + checkDigit);
+
+    // Combine and validate
+    String fullInput = baseInput + checkDigit;
+    boolean isValid = VerhoeffSnippet.validateVerhoeff(fullInput);
+    System.out.println("Generated check digit for input " + baseInput + " -> " + checkDigit);
+    System.out.println("Testing validateVerhoeff with full input: " + fullInput + " -> " + isValid);
+
+    assertTrue(isValid, "Expected " + fullInput + " to be valid, but it was not.");
+  }
+}