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Tanmay-Singh3004Tanmay-Singh3004
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Improvement: Removed main function from PalindromePrime class. Returned the output instead of just printing. Added JUnit tests
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‎DIRECTORY.md

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* [MedianOfMatrixtest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/misc/MedianOfMatrixtest.java)
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* [MedianOfRunningArrayTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/misc/MedianOfRunningArrayTest.java)
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* [MirrorOfMatrixTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/misc/MirrorOfMatrixTest.java)
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* [PalindromePrimeTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/misc/PalindromePrimeTest.java)
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* [PalindromeSinglyLinkedListTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/misc/PalindromeSinglyLinkedListTest.java)
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* [RangeInSortedArrayTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/misc/RangeInSortedArrayTest.java)
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* [ThreeSumProblemTest](https://github.com/TheAlgorithms/Java/blob/master/src/test/java/com/thealgorithms/misc/ThreeSumProblemTest.java)

‎src/main/java/com/thealgorithms/misc/PalindromePrime.java

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@@ -1,51 +1,114 @@
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package com.thealgorithms.misc;
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import java.util.Scanner;
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/**
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* Utility class for finding palindromic prime numbers.
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*
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* Palindromic primes are prime numbers that remain the same when their digits are reversed.
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*
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* For more information, refer to the
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* <a href="https://en.wikipedia.org/wiki/Palindromic_prime">Palindromic prime</a> Wikipedia page.
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*
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* <b>Example usage:</b>
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* <pre>
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* int[] palindromicPrimes = PalindromePrime.findPalindromicPrimes(5);
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* System.out.println(Arrays.toString(palindromicPrimes)); // Output: [2, 3, 5, 7, 11]
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*
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* int nthPalindromicPrime = PalindromePrime.findNthPalindromicPrime(5);
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* System.out.println(nthPalindromicPrime); // Output: 11
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* </pre>
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*/
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public final class PalindromePrime {
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private PalindromePrime() {
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}
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public static void main(String[] args) { // Main function
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Scanner in = new Scanner(System.in);
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System.out.println("Enter the quantity of First Palindromic Primes you want");
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int n = in.nextInt(); // Input of how many first palindromic prime we want
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functioning(n); // calling function - functioning
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in.close();
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private PalindromePrime() {
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// Private constructor to prevent instantiation
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}
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public static boolean prime(int num) { // checking if number is prime or not
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for (int divisor = 3; divisor <= Math.sqrt(num); divisor += 2) {
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if (num % divisor == 0) {
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return false; // false if not prime
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/**
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* Finds the first n palindromic prime numbers.
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*
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* @param n The number of palindromic primes to find
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* @return An array containing the first n palindromic prime numbers
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*/
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public static int[] findPalindromicPrimes(int n) {
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if (n == 0) {
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return new int[0];
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}
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int[] result = new int[n];
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result[0] = 2; // The first palindromic prime
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int count = 1;
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int num = 3;
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while (count < n) {
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if (num == reverse(num) && isPrime(num)) { // number is prime and its reverse is the same
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result[count] = num;
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count++; // counts check when to terminate while loop
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}
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num += 2; // increase iterator value by two
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}
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return true; // True if prime
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return result;
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}
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public static int reverse(int n) { // Returns the reverse of the number
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int reverse = 0;
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while (n != 0) {
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reverse *= 10;
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reverse += n % 10;
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n /= 10;
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}
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return reverse;
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}
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public static void functioning(int y) {
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if (y == 0) {
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return;
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/**
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* Finds the nth palindromic prime number.
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*
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* @param n The position of the palindromic prime to find
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* @return The nth palindromic prime number
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*/
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public static int findNthPalindromicPrime(int n) {
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if (n <= 0) {
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throw new IllegalArgumentException("n must be greater than 0");
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}
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if (n == 1) {
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return 2; // The first palindromic prime
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}
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System.out.print(2 + "\n"); // print the first Palindromic Prime
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int count = 1;
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int num = 3;
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while (count < y) {
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if (num == reverse(num) && prime(num)) { // number is prime and it's reverse is same
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while (count < n) {
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if (num == reverse(num) && isPrime(num)) { // number is prime and its reverse is the same
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count++; // counts check when to terminate while loop
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System.out.print(num + "\n"); // print the Palindromic Prime
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}
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num += 2; // inrease iterator value by two
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if (count < n) {
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num += 2; // increase iterator value by two
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}
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}
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return num;
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}
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/**
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* Checks if a number is prime.
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*
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* @param num The number to check
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* @return true if the number is prime, false otherwise
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*/
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private static boolean isPrime(int num) {
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if (num < 2) {
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return false;
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}
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if (num == 2) {
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return true;
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}
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if (num % 2 == 0) {
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return false;
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}
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for (int divisor = 3; divisor <= Math.sqrt(num); divisor += 2) {
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if (num % divisor == 0) {
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return false; // false if not prime
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}
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}
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return true; // true if prime
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}
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/**
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* Reverses the digits of a number.
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*
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* @param num The number to reverse
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* @return The reversed number
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*/
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private static int reverse(int num) {
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int reversed = 0;
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while (num != 0) {
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reversed = reversed * 10 + num % 10;
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num /= 10;
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}
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return reversed;
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}
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}

‎src/test/java/com/thealgorithms/misc/PalindromePrimeTest.java

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package com.thealgorithms.misc;
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import static org.junit.jupiter.api.Assertions.assertArrayEquals;
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import static org.junit.jupiter.api.Assertions.assertEquals;
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import static org.junit.jupiter.api.Assertions.assertThrows;
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import org.junit.jupiter.api.Test;
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/**
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* Unit tests for the PalindromePrime class.
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*/
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public class PalindromePrimeTest {
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/**
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* Test the findPalindromicPrimes method with a positive number.
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*/
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@Test
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public void testFindPalindromicPrimesPositive() {
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int[] result = PalindromePrime.findPalindromicPrimes(5);
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assertArrayEquals(new int[] {2, 3, 5, 7, 11}, result);
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}
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/**
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* Test the findPalindromicPrimes method with zero.
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*/
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@Test
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public void testFindPalindromicPrimesZero() {
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int[] result = PalindromePrime.findPalindromicPrimes(0);
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assertArrayEquals(new int[] {}, result);
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}
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/**
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* Test the findNthPalindromicPrime method with a positive number.
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*/
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@Test
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public void testFindNthPalindromicPrimePositive() {
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int result = PalindromePrime.findNthPalindromicPrime(5);
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assertEquals(11, result);
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}
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/**
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* Test the findNthPalindromicPrime method with one.
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*/
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@Test
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public void testFindNthPalindromicPrimeOne() {
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int result = PalindromePrime.findNthPalindromicPrime(1);
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assertEquals(2, result);
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}
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/**
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* Test the findNthPalindromicPrime method with zero.
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*/
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@Test
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public void testFindNthPalindromicPrimeZero() {
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assertThrows(IllegalArgumentException.class, () -> PalindromePrime.findNthPalindromicPrime(0));
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}
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/**
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* Test the findNthPalindromicPrime method with a negative number.
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*/
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@Test
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public void testFindNthPalindromicPrimeNegative() {
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assertThrows(IllegalArgumentException.class, () -> PalindromePrime.findNthPalindromicPrime(-1));
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}
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/**
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* Test the findPalindromicPrimes method with a large number.
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*/
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@Test
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public void testFindPalindromicPrimesLarge() {
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int[] result = PalindromePrime.findPalindromicPrimes(10);
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assertArrayEquals(new int[] {2, 3, 5, 7, 11, 101, 131, 151, 181, 191}, result);
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}
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/**
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* Test the findNthPalindromicPrime method with a large number.
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*/
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@Test
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public void testFindNthPalindromicPrimeLarge() {
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int result = PalindromePrime.findNthPalindromicPrime(10);
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assertEquals(191, result);
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}
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}

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