Leveret Lunch in Functional Kotlin

leveret.kt

data class Cell(val y: Int, val x: Int) {
    fun neighbors() = listOf(Cell(y, x - 1), Cell(y - 1, x), Cell(y, x + 1), Cell(y + 1, x)) // WNES
}

data class Garden(val cells: List<List<Int>>) {
    val nRows = cells.size
    val nCols = cells[0].size

    fun findCenterCells() = listOf(
        Cell((nRows - 1) / 2, (nCols - 1) / 2), // NW
        Cell((nRows - 1) / 2, (nCols - 0) / 2), // NE 
        Cell((nRows - 0) / 2, (nCols - 1) / 2), // SW
        Cell((nRows - 0) / 2, (nCols - 0) / 2), // SE
    )

    fun nextCell(coords: List<Cell>, carrots: Int = 0, seen: Set<Cell> = setOf()): Int =
        coords
            .filter { it.y in 0 until nRows && it.x in 0 until nCols }
            .filter { it !in seen }
            .maxByOrNull { cells[it.y][it.x] } // cell with max # of carrots, preferring first
            .let {
                if (it == null || cells[it.y][it.x] == 0) carrots
                else nextCell(it.neighbors(), carrots + cells[it.y][it.x], seen + it)
            }
}

with(
    Garden(
        listOf(
            listOf(9, 9, 9, 9),
            listOf(9, 3, 1, 0),
            listOf(9, 1, 4, 2),
            listOf(9, 9, 1, 0),
        )
    )
) { nextCell(findCenterCells()) }