public class Solution
extends Object
1218 - Longest Arithmetic Subsequence of Given Difference\.
Medium
Given an integer array `arr` and an integer `difference`, return the length of the longest subsequence in `arr` which is an arithmetic sequence such that the difference between adjacent elements in the subsequence equals `difference`.
A **subsequence** is a sequence that can be derived from `arr` by deleting some or no elements without changing the order of the remaining elements.
**Example 1:**
**Input:** arr = [1,2,3,4], difference = 1
**Output:** 4
**Explanation:** The longest arithmetic subsequence is [1,2,3,4].
**Example 2:**
**Input:** arr = [1,3,5,7], difference = 1
**Output:** 1
**Explanation:** The longest arithmetic subsequence is any single element.
**Example 3:**
**Input:** arr = [1,5,7,8,5,3,4,2,1], difference = -2
**Output:** 4
**Explanation:** The longest arithmetic subsequence is [7,5,3,1].
**Constraints:**
* 1 <= arr.length <= 105
* -104 <= arr[i], difference <= 104