[subhobroto]

> Or if there is a systematic approach to this problem

There is.

The whiteboard firing squad questions are pretty predictable once you do enough of them.

The very bad ones will ask directly from one of the popular sites. DFS/BFS/Invert Binary Tree/Coin Change/Hop Jump Skip/you know.

You have to learn it once and can regurgitate until you forget them again.

I am happy to help a fellow HN'er and work out some trial whiteboard interviews with you if you feel that would help.