---
tags: data_structure_python
---

# 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