Algorithm that receives a dictionary, converts it to a GET string, and is optimized for big data
Considered as an interview question, my response would be, "what do you mean by 'optimized for big data'?" Wikipedia says,


  Big data is a term for data sets that are so large or complex that traditional data processing applications are inadequate to deal with them


and it's not clear how this is related to the problem of converting a dictionary to a query string (which would normally be solved by calling urllib.parse.urlencode). So there seems to be a hidden requirement here. Or possibly the interviewer is confused. Either way, you need to go through the requirements capture and analysis process before starting to write code.