力扣 -- 1218. 最长定差子序列

参考代码：

class Solution {
public:int longestSubsequence(vector<int>& arr, int difference) {int n=arr.size();unordered_map<int,int> hash;//nums[i]绑定dp[i]hash[arr[0]]=1;int ret=1;for(int i=1;i<n;i++){int a=arr[i];int b=a-difference;hash[a]=hash[b]+1;ret=max(ret,hash[arr[i]]);}return ret;}
};