int beautifulTriplets(int d, vector<int> arr) {
    
    unordered_set<int> s(arr.begin(), arr.end()); 
    int c = 0;

    for (size_t i = 0; i < arr.size(); i++) {
        if (s.count(arr[i]) && 
            s.count(arr[i] + d) && 
            s.count(arr[i] + 2 * d)) 
        {
            c++;
        }
    }
    return c;

}