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Java Solution for LeetCode algorithm problems, continually updating
1027\. Longest Arithmetic Subsequence
Medium
Given an array `nums` of integers, return the **length** of the longest arithmetic subsequence in `nums`.
Recall that a _subsequence_ of an array `nums` is a list nums[i1], nums[i2], ..., nums[ik]
with 0 <= i1 < i2 < ... < ik <= nums.length - 1
, and that 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`