Maximum Number of Vowels in a Substring of Given Length

Given a string s and an integer k.

Return the maximum number of vowel letters in any substring of s with length k.

Vowel letters in English are (a, e, i, o, u).

Example 1:

Input: s = "abciiidef", k = 3
Output: 3
Explanation: The substring "iii" contains 3 vowel letters.

Example 2:

Input: s = "aeiou", k = 2
Output: 2
Explanation: Any substring of length 2 contains 2 vowels.

Example 3:

Input: s = "leetcode", k = 3
Output: 2
Explanation: "lee", "eet" and "ode" contain 2 vowels.

Example 4:

Input: s = "rhythms", k = 4
Output: 0
Explanation: We can see that s doesn't have any vowel letters.

Example 5:

Input: s = "tryhard", k = 4
Output: 1

Constraints:

• 1 <= s.length <= 10^5
• s consists of lowercase English letters.
• 1 <= k <= s.length

Solution

class Solution:
    def maxVowels(self, s: str, k: int) -> int:
        # Time complexity: O(n).
        # Space complexity: O(5) ~= O(1).
        m, beg, end = len(s), 0, 0
        vowels = set(['a', 'e', 'i', 'o', 'u'])
        maxi, count = 0, 0
        
        while end < m:
            
            if s[end] in vowels:
                count += 1
            
            if end-beg+1 >= k:
                maxi = max(maxi, count)
                if s[beg] in vowels:
                    count -= 1
                beg += 1
            
            end += 1
        
        return maxi