I had a colleague from my recent summer internship refer me to a friend who worked at Facebook. About a week later, a recruiter reached out to schedule a phone interview.

I had three interviews in total. The first was an initial screening interview over the phone with the recruiter, where we simply went over my CV for 30 minutes.

A few days later, she scheduled a Skype interview with an engineer from Menlo Park. The interview was technical, and I managed to solve one question just about on time, with a few minutes left for questions for the engineer before he had to run off.

I was surprised to see the next morning that they wanted to move forward and schedule a second interview with me. This time, it would be with another engineer, but over video conference. The interviewer was very kind and gave me a hint when I was moving in the wrong direction with my solution. Again, I managed to solve the solution just about on time, with a few minutes left for questions.

Given an array of n positive integers and a positive integer s, find the minimal length of a subarray of which the sum is ≥ s. If there isn't one, return 0 instead.