This interview happened in 2016 spring and was for 2016 summer. The whole process took a super long time. I submitted the application in the middle of February and got online coding email one month later. Another one month later (middle of April), I got the first telephone interview from a manager in Data Science team. He introduced his team and the problem they were trying to figure out. I presented my work but it didn't solve that kind of problem. The good thing was that he enjoyed the conversation and referred me to anther group. Then the technical interviews came soon. There were three back-to-back video interviews. The questions were not super hard. I figured them out and had friendly chats with Twitter engineers. The final round was another telephone interview with the manager (not the first one). It was basically about the introduction to the team and whether I was willing to join the team. I felt Twitter was a nice company and the project sounded pretty interesting, so I agreed. Then the HR call about the salary and boarding stuff.
Actually, I've already finished my internship in Twitter. I really love the company. The people are so nice and the environment is excellent. I strongly recommend Twitter.