Leetcode 1218. Longest definite difference subsequence

Give you an array of integers arr And an integer difference, Please find out and return to arr The length of the longest isochromatic subsequence in , The difference between adjacent elements in this subsequence is equal to difference .

Subsequence It means that without changing the order of the other elements , Remove from... By deleting some elements or not deleting any elements arr Derived sequence .

Example 1：

 Input ：arr = [1,2,3,4], difference = 1
 Output ：4
 explain ： The longest isochromatic subsequence is  [1,2,3,4].

Example 2：

 Input ：arr = [1,3,5,7], difference = 1
 Output ：1
 explain ： The longest arithmetic subsequence is any single element .

Example 3：

 Input ：arr = [1,5,7,8,5,3,4,2,1], difference = -2
 Output ：4
 explain ： The longest isochromatic subsequence is  [7,5,3,1].
 

Tips ：

• 1 <= arr.length <= 10^5
• -104 <= arr[i], difference <= 10^4

Code:

class Solution {
    
public:
    int longestSubsequence(vector<int>& arr, int difference) {
    
        int maxlen=1;
        map<int,int>mymap;
        pair<map<int, int>::iterator, bool> ret;
        map<int,int>::iterator it;
        for(int i=0;i<arr.size();i++)
        {
    
            int start=arr[i];
            
            if((it=mymap.find(arr[i]-difference))!=mymap.end())
            {
    
                continue;
            }
            ret=mymap.insert(pair<int,int>(arr[i],0));
            if(!ret.second)
                continue;
            
            
            
            int templen=1;
            for(int j=i+1;j<arr.size();j++)
            {
    
                if((start+difference)==arr[j])
                {
    
                    templen++;
                    start+=difference;
                    
                }
            }
            maxlen=max(templen,maxlen);
        }
        cout<<maxlen<<endl;
        
        return maxlen;
        
    }
};