Find longest substring with at least k repeats

Q: Find longest substring with at least k repeats

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Question

Longest substring where each character appears at least k times

You are given:

a string s consisting of lowercase English letters
an integer k

Return the length of the longest substring of s such that every distinct character in that substring appears at least k times within the substring.

If no such substring exists, return -1.

Notes / assumptions

A substring is contiguous.
If k <= 1 , the answer is len(s) .
You should handle edge cases like empty string, k > len(s) , and repeated characters.

Example

s = "aaabb", k = 3 → longest valid substring is "aaa" → return 3 .

Find longest substring with at least k repeats

Longest substring where each character appears at least k times

Notes / assumptions

Example

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