Citi Sales, Trading & Quantitative Analysis interview questions

I applied through the firm's website and I got an email to set up a phone interview. I was expecting to get a call from an analyst as that's usually the case for most of the bulge brackets, but I actually got a call from the VP of quantitative analysis group. It was an interesting interview as the structure was totally different in that he introduced himself and his group first and then I walked through my resume. After few fit questions, I was asked questions on programming, regression, brain teasers and stats questions. I found it very difficult.