kt: add «3208. Alternating Groups II»

URL:	https://leetcode.com/problems/alternating-groups-ii/
Signed-off-by: Matej Focko <me@mfocko.xyz>

kt/alternating-groups-ii.kt

@@ -0,0 +1,42 @@
+class Solution {
+    private data class Acc(val last: Int, val count: Int, val groups: Int) {
+        constructor(last: Int) : this(last, 1, 0)
+
+        fun update(
+            k: Int,
+            color: Int,
+        ): Acc {
+            val count =
+                when {
+                    color == last -> {
+                        1
+                    }
+                    else -> {
+                        count + 1
+                    }
+                }
+
+            val groups =
+                when {
+                    count >= k -> groups + 1
+                    else -> groups
+                }
+
+            return copy(
+                last = color,
+                count = count,
+                groups = groups,
+            )
+        }
+    }
+
+    fun numberOfAlternatingGroups(
+        colors: IntArray,
+        k: Int,
+    ): Int =
+        (1..colors.size + k - 2)
+            .map { i -> i % colors.size }
+            .fold(Acc(colors[0])) { acc, i ->
+                acc.update(k, colors[i])
+            }.groups
+}