Sergio Alves

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', and '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.

Constraints:

• 1 <= s.length <= 105
• s consists of lowercase English letters.
• 1 <= k <= s.length

PHP Code

class Solution {

    /**
     * @param String $s
     * @param Integer $k
     * @return Integer
     */
    function maxVowels($s, $k) {
        $s_array = str_split($s);
        $sum = 0;
        for ($i=0; $i<$k; $i++) {
            if (preg_match("/[aeiou]/i", $s_array[$i])) {
                $sum++;
            }
        }
        $result = $sum;
        
        for ($i=$k; $i<count($s_array); $i++) {
            if (preg_match("/[aeiou]/i", $s_array[$i])) {
                $sum++;
            }
            if (preg_match("/[aeiou]/i", $s_array[$i-$k])) {
                $sum--;
            }         
            if ($sum > $result) {
                $result = $sum;
            }
        }
        return $result;
    }
}