Ask HN: Coding interview advice or tuition/mentor

I have applied to large tech firms and do well in the interviews except fail at the hard coding interviews.

I am looking for resources, advice or even better a mentor/tutor that can help me improve and take me to the next stage (preferably someone who works at the top 4 tech firms and conducts interviews).

I have done a fair amount of practice on Leetcode and can do easy or medium questions including typical data structures and algorithms. However, I seem to fail at some hard questions which has stopped me passing at interviews. I would describe myself as a very competent programmer with good CS knowledge - though I have had no formal training.

You can directly contact me through my email which is in my HN profile.