1456. Maximum Number of Vowels in a Substring of Given Length - Explanation

class Solution:
    def maxVowels(self, s: str, k: int) -> int:
        vowel = {'a', 'e', 'i', 'o', 'u'}
        res = 0

        for i in range(len(s) - k + 1):
            cnt = 0
            for j in range(i, i + k):
                cnt += 1 if s[j] in vowel else 0
            res = max(res, cnt)

        return res

class Solution:
    def maxVowels(self, s: str, k: int) -> int:
        vowel = {'a', 'e', 'i', 'o', 'u'}
        prefix = [0] * (len(s) + 1)
        for i in range(len(s)):
            prefix[i + 1] = prefix[i] + (1 if s[i] in vowel else 0)

        res = 0
        for i in range(k, len(s) + 1):
            res = max(res, prefix[i] - prefix[i - k])

        return res

class Solution:
    def maxVowels(self, s: str, k: int) -> int:
        vowel = {'a', 'e', 'i', 'o', 'u'}

        l = cnt = res = 0
        for r in range(len(s)):
            cnt += 1 if s[r] in vowel else 0
            if r - l + 1 > k:
                cnt -= 1 if s[l] in vowel else 0
                l += 1
            res = max(res, cnt)
        return res

class Solution:
    def maxVowels(self, s: str, k: int) -> int:
        def getId(c):
            return ord(c) - ord('a')

        mask = (1 << getId('a')) | (1 << getId('e')) | \
               (1 << getId('i')) | (1 << getId('o')) | \
               (1 << getId('u'))

        l = cnt = res = 0
        for r in range(len(s)):
            cnt += ((mask >> getId(s[r])) & 1)
            if r - l + 1 > k:
                cnt -= ((mask >> getId(s[l])) & 1)
                l += 1
            res = max(res, cnt)
        return res