1297. Maximum Number of Occurrences of a Substring

This question asks to find the number of occurrences of a substring of at least length minSize with a maximum amount of letters occurring. To do so, create a set of windows through the string with size minSize, and if they have less than maxLetters items, increment the Counter of that item.

class Solution:
    def maxFreq(self, s: str, maxLetters: int, minSize: int, maxSize: int) -> int:
        c = Counter()
        for i in range(len(s) - minSize + 1):
            t = s[i:i+minSize]
            if len(set(t)) <= maxLetters:
                c[t] += 1
        return max(c.values()) if c else 0