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Grokking the Coding Interview Patterns in C++

Solution: Count Substrings With K-Frequency Characters II

Explore how to apply the sliding window technique to count all substrings in a string where at least one character appears at least k times. Understand how to manage character frequencies efficiently, shrink and expand the window, and implement an optimized algorithm with O(n) time complexity and constant space usage.

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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 ...