fun part1(grid: Grid) = (horizontal + vertical + diagonals)
    .flatMap { m -> grid.findAll('X').map { it to m } }
    .mapNotNull { (p, m) -> if (grid[p + m] == 'M') p + m to m else null }
    .mapNotNull { (p, m) -> if (grid[p + m] == 'A') p + m to m else null }
    .count { (p, m) -> grid[p + m] == 'S' }

fun part2(grid: Grid): Int = grid.findAll('A').count { p ->
    diagonals.count { m -> grid[p - m] == 'M' && grid[p + m] == 'S' } == 2
}

typealias Move = Pair<Int, Int>
val diagonals: Set<Move> = setOf(-1 to -1, -1 to 1, 1 to -1, 1 to 1)
val vertical: Set<Move> = setOf(-1 to 0, 1 to 0)
val horizontal: Set<Move> = setOf(0 to -1, 0 to 1)

typealias Pos = Pair<Int, Int>
operator fun Pos.plus(d: Move) = Pos(first + d.first, second + d.second)
operator fun Pos.minus(d: Move) = Pos(first - d.first, second - d.second)

typealias Grid = List<String>
operator fun Grid.get(p: Pos) = getOrNull(p.first)?.getOrNull(p.second)
fun Grid.findAll(ch: Char): List<Pos> = flatMapIndexed { r, line ->
    line.indices.filter { line[it] == ch }.map { c -> Pos(r, c) }
}