Amazon UK, on the first round of coding, i was being asked something like to build a treee from string, i am tried to impelement the logic but the interviewer was not helpfull

Loop — 4 rounds, all on the same day Round 1 — Coding (DSA) Interviewer was a senior SDE, very friendly. Warm-up + behavioral: "Tell me about a time you took ownership of something outside your responsibilities." Main question: Given a list of meeting intervals, find the minimum number of conference rooms required. I used a heap. He then asked a follow-up: what if meetings could be reassigned to minimize total idle time? We discussed approaches but didn't fully code it. He cared a lot about how I talked through edge cases out loud. Round 2 — Coding + Problem Solving LP question: "Describe a situation where you disagreed with a teammate." Coding: LRU Cache implementation from scratch. I used a hashmap + doubly linked list. He pushed on thread-safety and what happens at capacity 0. Round 3 — Behavioral (Bar Raiser) This was the toughest round — no coding, all Leadership Principles, very deep STAR-format probing. Questions I got: "Tell me about a time you failed and what you learned." "A time you had to deliver something with a tight deadline and limited information." The bar raiser kept drilling: "What was your specific contribution?" "What would you do differently?" "What data did you use?" Have 6–8 strong stories ready with metrics. Round 4 — Low-Level Design Design: Design a parking lot system (classes, vehicle types, spot allocation, pricing). Then he asked me to code the findSpot() and releaseSpot() methods.