class Solution {
    data class BoxType(val boxes: Int, val units: Int)
    fun toBoxType(x: IntArray): BoxType = BoxType(x[0], x[1])

    fun maximumUnits(boxTypes: Array<IntArray>, truckSize: Int): Int =
        boxTypes
        .map { toBoxType(it) }
        .sortedByDescending(BoxType::units)
        .fold(0 to 0) { acc, boxType ->
            if (acc.first < truckSize) {
                val count = minOf(truckSize - acc.first, boxType.boxes)

                (acc.first + count) to (acc.second + count * boxType.units)
            } else {
                acc
            }
        }
        .second
}