LinkedIn Sr. Software Engineer interview questions

I applied online and also with a recruiter. Standard process - set up a phone screening a couple of weeks out. The interviewer was definitely not the one listed in the email (possibly last minute replacement) and he must have been sitting in an open area at first; I had to mention the heavy background noise twice (I could hear voices, though not exact words, before he made his first adjustment). Because of the level I was asked a lot of platform (iOS) questions, primarily around threading, in a rapid-fire manner. I know I did well on the algorithms (saw a more complicated version of one of them before) and even had time at the end to discuss, but not code, a variant on one question. However, I supposedly did not answer the platform/threading questions fast enough so the hiring committee (for a phone screen) declined to invite me for an onsite. Very likely I would not have moved on regardless of the background noise, but it didn't help.

Telephonic Interview - 2 interviewers - 2 basic algo questions on strings. I answered both the questions in time. They wanted me to do better on time complexity on 2nd question, mine was O(n) time and O(1) space, since I had insertion of data in my hands. Then I spoke out the better way, half way coded it but there was no time to code it fully. According to me, I did really well. These guys are totally unpredictable and naive. 2 freshers test any level of experienced guys. They just have 1 solution in mind. You do it the other way, you are not getting it. They expect you to do 2 questions completely in the best ways (acc to them), at the same time it should be readable, maintenable, logical etc - everything.