LinkedIn Sr. Software Engineer interview questions

I was referred at LinkedIn. The recruitment team was prompt and very responsive to schedule changes. The lead recruiter was very informative on the phone and talked to me for half an hour explaining LinkedIn and understanding my interests. I was very impressed. First Phone Screen: Collabedit coding was expected with perfect language syntax Implement power function efficiently. Find maximum sum subset in an array with negative integers Second Phone Screen: Find if a string is a number or not. Repeat question of maximum sum subset. After telling them that I already answered this, they were surprised as the first interviewer had not left any notes! This was a hard problem which I had answered correctly. I was very disappointed. Variation of the same problem, maximum product subset. I faultered a bit and was not able to get to the right code. However my idea was correct.