LeetCode/kt/count-of-substrings-containing-every-vowel-and-k-consonants-ii.kt

class Solution {
    private fun isVowel(c: Char): Boolean = "aeiou".contains(c)

    private fun atLeastK(
        word: String,
        k: Int,
    ): Long {
        var substrings = 0L
        var (start, end) = 0 to 0

        val count = mutableMapOf<Char, Int>()
        var consonants = 0

        while (end < word.length) {
            val newLetter = word[end]

            when {
                isVowel(newLetter) -> count[newLetter] = 1 + (count.getOrDefault(newLetter, 0))
                else -> consonants++
            }

            while (count.size == 5 && consonants >= k) {
                substrings += word.length - end

                val startLetter = word[start]
                when {
                    isVowel(startLetter) && count[startLetter] == 1 -> count.remove(startLetter)
                    isVowel(startLetter) -> count[startLetter] = count[startLetter]!! - 1
                    else -> consonants--
                }

                start++
            }

            end++
        }

        return substrings
    }

    fun countOfSubstrings(
        word: String,
        k: Int,
    ): Long = atLeastK(word, k) - atLeastK(word, k + 1)
}