Goldman Sachs, Associate Interview Experience - USA (Salt Lake City) - rejected

I was refered to the postion by a friend. Got email after a month for Coderpad.

CoderPad Round:

1. Check if a number is Power of 10.
2. Provided student name scores, find the highest average grade in the class.

After 2 weeks I got the result and was selected for next rounds. All the 3 rounds back to back on same day.

Round 1 : DSA

1. Asked few questions around my work/resume and how my day to day work like.
2. Coding : Given a dictionary ={ cat, zat, force, zebra} and char Array = {a, c ,a ,k,z, e, t}, what is the longest word that can be formed. I though I might be able to use Trie for optmization, big mistake. This problem is has simple solution with freq map/count. I did provide that solution, but I was hung up on finding optimal solution, which might have ticked off the interviewer.

Round 2: Software Design They straight jumped to question: Design Twitter to post and Search tweets. Questions around what I did and why I built is that way. SQL/NoSQL etc etc.

Round 3: SDLC and resume: Just grilling around my resume and day to day work.

I was not confident on the interview I gave, It couldn't have been easier, yet I wasn't able to give my best. After 3 weeks got rejection email.