LeetCode/kt/alternating-groups-ii.kt

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
}