class Solution { public: int arithmeticTriplets(vector<int>& nums, int diff) { int n=nums.size(); set<int> s(nums.begin(),nums.end()); int ans=0; for(int i=0;i<n;i++) { if(s.find(nums[i]-diff)!=s.end() && s.find(nums[i]-2*diff)!=s.end()) { ans++; } } return ans; } };