The "Longest Repeating Character Replacement" question is one of those string manipulation problems that sneak up on you. At first glance, it seems like a counting or brute-force challenge, but the optimal solution leans heavily on sliding window and frequency analysis. It’s a fantastic warm-up for mastering problems involving substrings and character frequency tracking, common themes in many real-world parsing and formatting systems.

The Minimum Size Subarray Sum problem is a great example of using the sliding window technique to solve a real-world scenario - finding the smallest set of contiguous actions or values that meet a threshold. It helps build your skills with optimizing time and space over brute-force solutions and comes up frequently in interviews at all levels.

The Longest Substring Without Repeating Characters problem is one of those warm-up problems that seems deceptively simple but teaches you a ton about sliding window techniques and string manipulation. It shows up frequently in interviews and also mimics real-world cases like processing tokens or user input where uniqueness matters.