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Grokking the Coding Interview Patterns in C#

Solution: Count Substrings With K-Frequency Characters II

Explore how to use the sliding window technique to efficiently count substrings where at least one character appears at least k times. Understand the algorithm's use of two pointers and frequency tracking to optimize performance and reduce complexity.

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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 ...