Solution: Count Substrings With K-Frequency Characters II

Explore how to count all substrings in a string where at least one character appears at least k times. Understand the sliding window approach to efficiently track character frequencies, expand and shrink the window, and avoid brute force methods. Gain insight into managing time and space complexity through a hands-on example that improves substring problem-solving skills using a fixed-size frequency array and two-pointer technique.