I answered the question by implementing the email spam detection algorithm in C++ as follows: Normalize Case: You converted all spam words and email subjects to lowercase to ensure case-insensitive matching. Efficient Lookup: You stored the spam words in an unordered set to allow for quick lookups. Word Counting: For each email subject, you split the string into individual words and checked how many of those words matched the spam words from the list. Spam Detection: If two or more spam words were found in the subject, you marked the email as "spam"; otherwise, it was marked as "not_spam." The solution was efficient and handled the constraints well, ensuring fast performance even with large inputs.