The interview process began with email correspondence and an introduction, followed by a phone screen with a recruiter. Finally, a 45-minute technical interview with an engineer took place, which included coding exercises.

The phone screen was laid-back and informal.

The technical interview was conducted over the phone, utilizing a collaborative web text editor for the coding exercises, and was fairly difficult.

The entire process spanned almost two weeks.

From a tree, get a list of lists of integers. Each inner list corresponds to all integers at depth 'i' from the root.