leetcode 395. Longest Substring with At Least K Repeating Characters

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Find the length of the longest substring T of a given string (consists of lowercase letters only) such that every character in T appears no less than k times.

Example 1:


Input:
s = “aaabb”, k = 3
Output:
3
The longest substring is “aaa”, as ‘a’ is repeated 3 times.

Example 2:


Input:
s = “ababbc”, k = 2
Output:
5
The longest substring is “ababb”, as ‘a’ is repeated 2 times and ‘b’ is repeated 3 times.

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class Solution(object):
    def longestSubstring(self, s, k):
        """
        :type s: str
        :type k: int
        :rtype: int
        """
        for c in set(s):
            if s.count(c) < k:
                return max(self.longestSubstring(t,k) for t in s.split(c))
        return len(s)