kt: add «3306. Count of Substrings Containing Every Vowel and K Consonants II»

URL:	https://leetcode.com/problems/count-of-substrings-containing-every-vowel-and-k-consonants-ii/
Signed-off-by: Matej Focko <me@mfocko.xyz>

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

@@ -0,0 +1,45 @@
+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)
+}