How To Prepare for Technical Interview at Facebook

The highlight was seeing a live demonstration of their Technical Interview process in which a presenter/developer whiteboarded a solution in front of a 100+ person audience. In an actual 5–6 hour Facebook interview, roughly half the time will be spent completing coding challenges. As a result, it was emphasized that candidates use the time to put their best foot forward.

At Facebook, candidates are given approximately 45 minutes to solve each coding question. Given the time constraint, they suggest making an impression by asking the right questions, then proceeding to implement a brute force approach before optimizing your design. Solving challenges using specific API’s or language features are also accepted, as long as you’re able to explain in detail how they perform. To demonstrate, let’s revisit a code challenge on creating an algorithm to detect unique characters in a String. The signature is as follows:

As with most code, there are many possible approaches. In the article, I review how it can be solved by applying a brute force approach, then proceed to optimize the code so that it runs in linear time — O(n) or better. What wasn’t discussed was solving it purely with native Swift API’s or language features. Interestingly, this seemingly concise solution also satisfies our requirement:

At first glance, the code looks fabulous, but is it indeed the best answer? More importantly, given the stress of a typical interview, would one have the ability to prove or disprove its efficiency? The lesson being — focus less on syntax and instead, work toward showcasing your knowledge by proving your approach.

Liked this essay? Read and discover my Swift Algorithms Book on Medium.

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