1218. 最长定差子序列

class Solution:
   def longestSubsequence(self, arr: List[int], difference: int) -> int:
       func = {arr[0]: 1}
       for i in range(1, len(arr)):
           if arr[i] - difference in func:
               func[arr[i]] = func[arr[i] - difference] + 1
           else:
               func[arr[i]] = 1
       return max(func.values())