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Solution: Count Substrings With K-Frequency Characters II

Explore the sliding window technique to efficiently count substrings with at least one character appearing exactly k times. Understand how to maintain frequency counts, adjust window boundaries, and achieve an optimal O(n) solution. This lesson guides you step-by-step through the problem-solving process and complexity analysis.

Statement

Given a string s and an integer k, return the total number of substrings of s where at least one character appears at least k times.

Note: A substring is a contiguous sequence of characters within a string. For example, "edu" is a substring of "educative". 

Constraints:

  • 11 \leq ...