diff --git a/src/main/java/com/thealgorithms/maths/CatalanNumbers.java b/src/main/java/com/thealgorithms/maths/CatalanNumbers.java new file mode 100644 index 000000000..387756bdf --- /dev/null +++ b/src/main/java/com/thealgorithms/maths/CatalanNumbers.java @@ -0,0 +1,39 @@ +package com.thealgorithms.maths; + +/** + * Calculate Catalan Numbers + */ +public final class CatalanNumbers { + private CatalanNumbers() { + } + + /** + * Calculate the nth Catalan number using a recursive formula. + * + * @param n the index of the Catalan number to compute + * @return the nth Catalan number + */ + public static long catalan(final int n) { + if (n < 0) { + throw new IllegalArgumentException("Index must be non-negative"); + } + return factorial(2 * n) / (factorial(n + 1) * factorial(n)); + } + + /** + * Calculate the factorial of a number. + * + * @param n the number to compute the factorial for + * @return the factorial of n + */ + private static long factorial(final int n) { + if (n == 0 || n == 1) { + return 1; + } + long result = 1; + for (int i = 2; i <= n; i++) { + result *= i; + } + return result; + } +} diff --git a/src/test/java/com/thealgorithms/maths/CatalanNumbersTest.java b/src/test/java/com/thealgorithms/maths/CatalanNumbersTest.java new file mode 100644 index 000000000..2248ffd93 --- /dev/null +++ b/src/test/java/com/thealgorithms/maths/CatalanNumbersTest.java @@ -0,0 +1,43 @@ +package com.thealgorithms.maths; + +import static org.junit.jupiter.api.Assertions.assertEquals; +import static org.junit.jupiter.api.Assertions.assertThrows; + +import java.util.stream.Stream; +import org.junit.jupiter.api.Test; +import org.junit.jupiter.params.ParameterizedTest; +import org.junit.jupiter.params.provider.MethodSource; + +/** + * Test class for CatalanNumbers + */ +class CatalanNumbersTest { + + /** + * Provides test data for the parameterized Catalan number test. + * Each array contains two elements: + * [input number, expected Catalan number for that input] + */ + static Stream catalanNumbersProvider() { + return Stream.of(new Object[] {0, 1}, new Object[] {1, 1}, new Object[] {2, 2}, new Object[] {3, 5}, new Object[] {4, 14}, new Object[] {5, 42}, new Object[] {6, 132}, new Object[] {7, 429}, new Object[] {8, 1430}, new Object[] {9, 4862}, new Object[] {10, 16796}); + } + + /** + * Parameterized test for checking the correctness of Catalan numbers. + * Uses the data from the provider method 'catalanNumbersProvider'. + */ + @ParameterizedTest + @MethodSource("catalanNumbersProvider") + void testCatalanNumbers(int input, int expected) { + assertEquals(expected, CatalanNumbers.catalan(input), () -> String.format("Catalan number for input %d should be %d", input, expected)); + } + + /** + * Test for invalid inputs which should throw an IllegalArgumentException. + */ + @Test + void testIllegalInput() { + assertThrows(IllegalArgumentException.class, () -> CatalanNumbers.catalan(-1)); + assertThrows(IllegalArgumentException.class, () -> CatalanNumbers.catalan(-5)); + } +}