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

class Solution {
    public int maxVowels(String s, int k) {
        int vowelCount = 0, i = 0;
        for (; i < k; i++)
            if (isVowel(s.charAt(i)))
                vowelCount++;
        int maxCount = vowelCount;
        for (; i < s.length(); i++) {
            if (isVowel(s.charAt(i)))
                vowelCount++;
            if (isVowel(s.charAt(i - k)))
                vowelCount--;
            maxCount = Math.max(maxCount, vowelCount);
        }
        return maxCount;
    }

    public boolean isVowel(char c) {
        if (c == 'a' || c == 'e' || c == 'i' || c == 'o' || c == 'u')
            return true;
        return false;
    }
}