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Solution: Count Substrings With K-Frequency Characters II

Explore the sliding window method to efficiently count substrings that contain at least one character appearing k times or more. This lesson guides you through maintaining frequency counts and adjusting window boundaries to solve the problem in linear time while using constant extra space.

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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:

  • 1≤1 \leq s.length ≤3×103\leq 3 \times 10^{3}

  • 1≤1 \leq k ...