Apple Sr Software Engineer interview questions

Open position in Search team. Had two telephonic coding rounds before being called for onsite interview. 1st telephonic round coding question like Tree Serialize and deserialize, follow up question can the serialize string output be further compressed (which I didn’t have much time) . Then got an email from recruiter saying they want to have one more telephonic online coding round. In the second round coding problem asked was 3 sum problem with target equal to 0 and follow up was to find all possible combinations of subsets which equals target sum. Later next day got email from recruiter saying team wants to move forward with onsite interview. All the communication with regards to scheduling or any updates is done via email recruiter didn’t call to inform or have even the initial introductory call. Onsite interview email didn’t have any details apart from location and from and to time and hr contact name. Onsite interview every person who interview will give a coding question 1st round - with Engineer question like How will you identify performance problem in java application and one coding question 2nd round- with Engineer coding question like given k sorted lists get top n elements based on search score (like merge k sorted lists and select top n elements) 3rd round - with head of the team asked some general questions and then asked couple of questions like dfs coding and how to generate synonyms for search query (this question is very vague basically idea is to look at the log or user interactions in given user session time like say 10 sec and use that info to generate synonyms) 4th round lunch round with entire team , felt like they were trying to access if the potential candidate fits in the team dynamic 5th round with hiring manager general info about company and team praising about the company and informing that the potential candidate that it’s not 9-5 job and later asked coding question like sort 3 unique numbers (hint 2 pointers) 6th round with Engineer asked about coding problem like k dimensional tree or point problem not able to recollect 7th round with Engineer started to explain about employee org chat problem what data structure and if employee view manager (direct or in direct like skip level) then the profile should be colored red, if manager views direct or indirect reportee then profile color should be green else for other case blue color. Need to code data preprocessing and other logic Next couple of day later got email from recruiter informing about team passing.