Eltropy Senior Java Developer interview questions

R1: - 2 medium level leetcode problems (30 mins and 45 mins) R2: - Questions about experience, whats and whys - Given a function sendMessage(sender, message), how to implement scheduled message functionality R3: - How does concurrent hashmap work? - What is https and explain its working and benefit - What is jwt auth? What is oAuth? - What are spring interceptors and filters and what's the difference. R4: Given a system, say twitter, how to create a blacklist checking mechanism. For each country, see whether govt has blacklisted the IP using a govt provided API that returns yes/no when IP is provided. If an IP is blacklisted, don't allow access to the system. Blacklist updates every 24 hours. What's the best implementation for scale?