Google Software Engineer(Internship) interview questions

I applied through a referral. It took 2 weeks for them to reply and set up 2 phone interviews. The interviewers asked some algorithm and design questions that are not too hard, but I screwed up the first one.

There are two sessions of 45 minutes each with two different software engineers. The interviewers describe the problem on shared Google doc and ask for the optimum solutions first before you proceed for the brute-force solution. Then the interviewer asks for the complexity of the algorithm that you are going to design. And finally the best solution proceed with coding.