First an on-campus interview, where the guy was very friendly and gave some brainteasers

Then a phone interview, with some more math and computer science problems

The final round, an on-site interview, consisted of a 2.5 hour written test, mostly on programming, and then a bunch of 1 on 1 interviews. Friendliness of interviewers was on both ends of the spectrum

There are 10 red, 11 blue, 12 green chameleons. Sometimes, two chameleons meet. If they are the same color, nothing happens. If they are different colors, they will both change to the third color. Can all chameleons ever be the same color?

There are 25 horses. You get to race them 5 at a time, determining relative ranking. How many races does it take to figure out the top 3?