Longest vowel

fun main() {
    val validSequenceLetters = charArrayOf('a', 'e', 'i', 'o', 'u')

    fun CharSequence.startsAndEndsWithCorrectLetter(): Boolean {
        return firstOrNull() == validSequenceLetters.first() && last() == validSequenceLetters.last()
    }

    val string = "dfgaeioozuaeiooua"

    val sb = StringBuilder()
    var longestVowel = 0;

    for (char in string) {
        if (sb.isNotEmpty() && (sb.last() > char || char !in validSequenceLetters)) {
            if (sb.startsAndEndsWithCorrectLetter()) {
                longestVowel = sb.length
            }
            sb.clear()
        }
        sb.append(char)
    }
    if (sb.startsAndEndsWithCorrectLetter()) {
        longestVowel = sb.length
    }

    println(longestVowel)
}