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.
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 <= 10^5-10^4 <= arr[i], difference <= 10^4