Prezi Full Stack Web Developer interview questions

I applied via the web site. They asked me to complete a programming challenge online (basically it was a binary search tree implementation and a subset search). The response was quite slow, it took almost three weeks to rate my test. Then I went in for a 1:1 interview with a senior developer. He asked the following questions: - Imagine a triangle, in each vertex an ant is sitting. Ants can walk freely from one vertex to the other. What is the possibility that two ants will start walking and collide? What if we consider an n-vertex polygon? - Describe how you would implement an LRU cache? (He also asked about the runtime complexity of various operations.) - What is a hash function? - What is a singleton? What is the problem with it? - Describe dependency injection - If you were given a log file of 1 TB, how would you process it? (E.g. find the 10 most frequently opened prezis on a day) - What is a global variable? Why don't we use global variable all over the place?