题目描述：

 

 

class Solution:
    def longestSubsequence(self, arr: List[int], difference: int) -> int:
        dp = dict()
        for a in arr:
            pre = a - difference
            if pre in dp:
                dp[a] = max(dp.get(a, 0), dp[pre] + 1)
            else:
                dp[a] = 1
        return max([x for _, x in dp.items()])