Given a set of integers in an array arr[] of size n , write a program to find the length of the longest arithmetic subsequence in arr[].

Problem Note

• Arithmetic Progression is a sequence in which all the differences between consecutive pairs are the same, i.e sequence P[0], P[1], P[2], …, P[m - 1] of length m is an Arithmetic Progression if and only if P[1] - P[0] == P[2] - P[1] == P[3] - P[2] == … == P[m - 1] - P[m - 2]
• The common difference can be positive, negative or 0.

Example 1

Input: arr[] = [2, 6, 10, 14]
Output: 4
Explanation: [2, 6, 10, 14] form an arithmetic progression with common difference 4.

Example 2

Input: arr[] = [2, 4, 8, 2, 12]
Output: 3
Explanation:[4, 8, 12] form an arithmetic progression.