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Solution: Count Substrings With K-Frequency Characters II

Explore how to use the sliding window technique to count all substrings where any character appears at least k times in a string. Understand the approach of dynamically expanding and shrinking the window while tracking character frequencies, leading to an efficient O(n) time complexity solution suitable for coding interviews.

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 ...