Adds Longest Arithmetic Subsequence Implementation (#5501)

* Added LongestArthmeticSubsequence

---------

Co-authored-by: Piotr Idzik <65706193+vil02@users.noreply.github.com>

src/test/java/com/thealgorithms/dynamicprogramming/LongestArithmeticSubsequenceTest.java

@@ -0,0 +1,35 @@
+package com.thealgorithms.dynamicprogramming;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+import java.util.stream.Stream;
+import org.apache.commons.lang3.ArrayUtils;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.Arguments;
+import org.junit.jupiter.params.provider.MethodSource;
+
+public class LongestArithmeticSubsequenceTest {
+    @ParameterizedTest
+    @MethodSource("provideTestCases")
+    void testGetLongestArithmeticSubsequenceLength(int[] nums, int expected) {
+        assertEquals(expected, LongestArithmeticSubsequence.getLongestArithmeticSubsequenceLength(nums));
+    }
+    @ParameterizedTest
+    @MethodSource("provideTestCases")
+    void testGetLongestArithmeticSubsequenceLengthReversedInput(int[] nums, int expected) {
+        ArrayUtils.reverse(nums);
+        assertEquals(expected, LongestArithmeticSubsequence.getLongestArithmeticSubsequenceLength(nums));
+    }
+
+    @Test
+    void testGetLongestArithmeticSubsequenceLengthThrowsForNullInput() {
+        assertThrows(IllegalArgumentException.class, () -> LongestArithmeticSubsequence.getLongestArithmeticSubsequenceLength(null));
+    }
+
+    private static Stream<Arguments> provideTestCases() {
+        return Stream.of(Arguments.of(new int[] {3, 6, 9, 12, 15}, 5), Arguments.of(new int[] {1, 7, 10, 13, 14, 19}, 4), Arguments.of(new int[] {1, 2, 3, 4}, 4), Arguments.of(new int[] {}, 0), Arguments.of(new int[] {10}, 1), Arguments.of(new int[] {9, 4, 7, 2, 10}, 3),
+            Arguments.of(new int[] {1, 2, 2, 2, 2, 5}, 4));
+    }
+}