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Solution: Count Substrings With K-Frequency Characters II

Explore how to use the sliding window technique to count all substrings of a string where at least one character occurs k times. Understand how two pointers track character frequencies and how the algorithm expands and shrinks windows for optimal performance. This lesson enables you to write an O(n) time and O(1) space solution to substring frequency problems.

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 ...