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Adds Longest Arithmetic Subsequence Implementation (#5501)
* Added LongestArthmeticSubsequence --------- Co-authored-by: Piotr Idzik <65706193+vil02@users.noreply.github.com>
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package com.thealgorithms.dynamicprogramming;
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import java.util.HashMap;
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final class LongestArithmeticSubsequence {
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private LongestArithmeticSubsequence() {
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}
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/**
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* Returns the length of the longest arithmetic subsequence in the given array.
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*
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* A sequence seq is arithmetic if seq[i + 1] - seq[i] are all the same value
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* (for 0 <= i < seq.length - 1).
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*
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* @param nums the input array of integers
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* @return the length of the longest arithmetic subsequence
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*/
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public static int getLongestArithmeticSubsequenceLength(int[] nums) {
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if (nums == null) {
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throw new IllegalArgumentException("Input array cannot be null");
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}
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if (nums.length <= 1) {
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return nums.length;
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}
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HashMap<Integer, Integer>[] dp = new HashMap[nums.length];
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int maxLength = 2;
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// fill the dp array
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for (int i = 0; i < nums.length; i++) {
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dp[i] = new HashMap<>();
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for (int j = 0; j < i; j++) {
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final int diff = nums[i] - nums[j];
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dp[i].put(diff, dp[j].getOrDefault(diff, 1) + 1);
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maxLength = Math.max(maxLength, dp[i].get(diff));
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}
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}
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return maxLength;
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}
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}
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package com.thealgorithms.dynamicprogramming;
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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 java.util.stream.Stream;
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import org.apache.commons.lang3.ArrayUtils;
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import org.junit.jupiter.api.Test;
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import org.junit.jupiter.params.ParameterizedTest;
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import org.junit.jupiter.params.provider.Arguments;
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import org.junit.jupiter.params.provider.MethodSource;
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public class LongestArithmeticSubsequenceTest {
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@ParameterizedTest
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@MethodSource("provideTestCases")
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void testGetLongestArithmeticSubsequenceLength(int[] nums, int expected) {
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assertEquals(expected, LongestArithmeticSubsequence.getLongestArithmeticSubsequenceLength(nums));
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}
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@ParameterizedTest
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@MethodSource("provideTestCases")
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void testGetLongestArithmeticSubsequenceLengthReversedInput(int[] nums, int expected) {
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ArrayUtils.reverse(nums);
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assertEquals(expected, LongestArithmeticSubsequence.getLongestArithmeticSubsequenceLength(nums));
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}
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@Test
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void testGetLongestArithmeticSubsequenceLengthThrowsForNullInput() {
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assertThrows(IllegalArgumentException.class, () -> LongestArithmeticSubsequence.getLongestArithmeticSubsequenceLength(null));
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}
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private static Stream<Arguments> provideTestCases() {
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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),
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Arguments.of(new int[] {1, 2, 2, 2, 2, 5}, 4));
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}
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}
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