Longest Substring with At Least K Repeating Characters.py

'''
 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.

'''

class Solution(object):
    def longestSubstring(self, s, k):
        """
        :type s: str
        :type k: int
        :rtype: int
        """
        if len(s) < k:
            return 0
        for c in s:
            if s.count(c) < k:
                return max(self.longestSubstring(x, k) for x in s.split(c))
            
        return len(s)