Welcome to your interview.
The question is on your right: Merge Large Datasets Safely. Take a moment with it first.
Talk your thinking through with me if you like - when you're confident, submit your answer and I'll grade it like a real screen (7/10 or better passes). Discussion and graded submissions share your five interviewer interactions, so spend them well.
Write a script to merge two large datasets on a common key at Synchrony, handling missing values and mismatched data types without blowing up the memory footprint.