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;
    }
};