I took an hour long online coding challenge through Hackerrank with two questions that were pretty easy. I heard back in a few days and had a 45 minute phone interview also hosted through Hackerrank. My interviewer first asked about my resume and projects and then gave me one technical coding problem.
Interview questions [1]
Question 1
Display the number of retweets a tweet gets using 4 characters total with max one position past the decimal point in US and Indonesian standard (eg 1.5 b, 3.2k)
One of the worst interview experiences I've had with a company. Recruiter sent me a generic email for a coding challenge that didn't even include my name in the greetings. Coding challenge was pretty straightforward, but was all about optimizing to the fastest solution (passed 12/14 tests). Followed up with recruiter 3 separate times and never got a response or even rejection letter. My experience with Twitter employees has been very negative overall. They've all seemed very pretentious and had a "I'm too good for you and don't have time for you attitude". Come on man, Twitter's a dying company anyways, get over yourself. I'm sure you have time to respond to an email :)
I applied online. The process took 3 weeks. I interviewed at X in Mar 2015
Interview
I had one online coding challenge followed up by 2 phone interviews. Both of them were technical, asking Algorithm questions which are similar to the questions you can easily find online. The recruiter and interviewers were really nice, but one of the interviewer seemed he didn't like his current project at Twitter saying that only interns get to work on cool projects.