Leetcode-5214 Longest Arithmetic Subsequence of Given Difference(最长定差子序列)

typedef long long ll;
typedef pair<int,int> P;
#define _for(i,a,b) for(register int i = (a);i < b;i ++)
#define _rep(i,a,b) for(register int i = (a);i > b;i --)
#define INF 0x3f3f3f3f
#define MOD 100000000
#define maxn 10003


class Solution
{
    map<int,int> m;
    public:
        int longestSubsequence(vector<int>& arr, int difference)
        {
            int ans = 1;
            _for(i,0,arr.size())
            {
                auto iter = m.find(arr[i]-difference);
                if(iter==m.end())
                    m[arr[i]] = 1;
                else
                {
                    int k = iter->second;
                    m[arr[i]] = k+1;
                    ans = max(ans,k+1);
                }
            }
            return ans;
        }
};