I'm uploading my solutions for educational purposes only. If you're referencing this as you try to complete the challenge yourself, that's a poor choice—you should consider attempting this challenge honestly to get the best experience out of it.
foo.bar is a secret web tool used by Google to recruit new employees based on what they search for online. You can read more about the challenge on IBTimes, Medium, and Quora. I've triggered the prompt twice by searching for python list comprehension and use after free. Each time, the page split open to reveal the message, "You're speaking our language. Up for a challenge?"
The challenges increase in difficulty and allotted time (ranging from a day to a few weeks) with each level. Your code is run against hidden test cases which test both its execution speed and its memory efficiency. In my experience, a higher level also meant that the problem required more knowledge of common algorithms in order to solve them. I worked on foo.bar over the course of a month while juggling other coursework for my job.
After completing three levels, I was prompted to share my contact information with a Google recruiter. I waited a few weeks—I assume my solutions were being reviewed during this time—before I received an email from a Google recruiter saying, "I'm genuinely interested in learning more about your current situation and where you envision your career trajectory long-term."
