Not able to solve this question

#1

Hii…
I am trying to solve this D.P based question.
1027. Longest Arithmetic Subsequence
I am getting some logic…Related to LIS…
But not able to reach to a proper final logic.
Could you suggest me something for thid.
Thanks

#2

hello @ashishnnnnn

this is also somewhat similar to lis.
think in terms of common difference