Phenom Product Development Engineer interview questions

Firstly they conducted an online test as screening test and I have cleared it and next day they conducted 2 Technical Rounds of interview mainly concentrating on data structures and algorithms and they have sent offer letters for the selected candidates

one technical round , Hr approached me for the position then he schedule the interview , He asked few java basic questions and then he asked design pattern questions which was tricky, And I guess interviewer don't that if you ask hard question you have to give atleast 45 minutes for the question but he gave me 20 mins to solve Reverse Nodes in K- Group problem, which is leetcode hard problem I solved the problem , and I don't know what he was thinking that being a start up he asked that hard question and pay is also not equal to google or amazon but expecting a lot.