Microsoft Senior Developer interview questions

What are some examples of challenges that you had to develop new approaches to overcome?

This was scheduled for 5 rounds. 3 rounds were in Data structures and algorithms which were of mid level complexity. Please do remember that they are looking at your approach. Don't jump in to solutions. Build your algorithm. One interview was on my current project and how i would build it differently. The last interview was a design question where i had to build a Monopoly game.