I got into the first round of interviewing with the team through a recruiter.

There were two or three engineers on the call interviewing me; one of them was a senior engineer.

They asked me to talk through basic approaches to building algorithms, with an emphasis on Big O concepts in computational power and memory usage. To the tune of: you are writing a method, it takes one parameter, and the parameter is an array of integers. There is one duplicate integer in the array. How would you build the method such that it finds the duplicate? Describe that using the best approaches for traversing the array, and the best data structures if you use any additional data structures. The following questions added more levels of complexity, where you would need an extra data structure, depending on what you wanted to accomplish.