int beautifulTriplets(int d, vector<int> arr) 
{
    size_t n = arr.size(), i = 0, nbt = 0;
    vector<size_t> bd(n);
    for(i = 0; i < n; i++) {
        auto lb = lower_bound(arr.begin(), arr.end(), arr[i]+d);
        if(lb != arr.end() && (*lb) == arr[i]+d) 
            bd[i] = lb - arr.begin();
    }    
    for(i = 0; i < n; i++) 
        if(bd[i] && bd[bd[i]]) 
            ++nbt;
    return nbt;            
}