1218. Longest Arithmetic Subsequence of Given Difference

link

class Solution:
    def longestSubsequence(self, arr: List[int], difference: int) -> int:
        
        n = len(arr)

        if n == 1:
            return 1

        M = defaultdict(lambda: 0)


        res = 0

        for i in range(n):
            M[arr[i]] = M[arr[i] - difference] + 1

            res = max(res, M[arr[i]])

        return res