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Kotlin-based LeetCode algorithm problem solutions, regularly updated
1027\. Longest Arithmetic Subsequence
Medium
Given an array `nums` of integers, return _the length of the longest arithmetic subsequence in_ `nums`.
**Note** that:
* A **subsequence** is an array that can be derived from another array by deleting some or no elements without changing the order of the remaining elements.
* A sequence `seq` is arithmetic if `seq[i + 1] - seq[i]` are all the same value (for `0 <= i < seq.length - 1`).
**Example 1:**
**Input:** nums = [3,6,9,12]
**Output:** 4 **Explanation: ** The whole array is an arithmetic sequence with steps of length = 3.
**Example 2:**
**Input:** nums = [9,4,7,2,10]
**Output:** 3 **Explanation: ** The longest arithmetic subsequence is [4,7,10].
**Example 3:**
**Input:** nums = [20,1,15,3,10,5,8]
**Output:** 4 **Explanation: ** The longest arithmetic subsequence is [20,15,10,5].
**Constraints:**
* `2 <= nums.length <= 1000`
* `0 <= nums[i] <= 500`