fun product(
xs: Sequence,
ys: Sequence,
): Sequence> = xs.flatMap { x -> ys.map { y -> x to y } }
fun product(
xs: Iterable,
ys: Iterable,
): Sequence> = product(xs.asSequence(), ys.asSequence())
class Solution {
fun runBFS(
grid: Array,
coords: Pair,
): Int {
val queue = ArrayDeque>()
queue.addLast(coords)
var size = 0
while (!queue.isEmpty()) {
val (y, x) = queue.removeFirst()
if (grid[y][x] != 1) {
continue
}
for ((dy, dx) in sequenceOf(0 to 1, 1 to 0, 0 to -1, -1 to 0)) {
if (!(y + dy in grid.indices) || !(x + dx in grid[y + dy].indices)) {
continue
} else if (grid[y + dy][x + dx] != 1) {
continue
}
queue.addLast(y + dy to x + dx)
}
// mark it as done
grid[y][x] = 0
size++
}
return size
}
fun maxAreaOfIsland(grid: Array): Int = product(grid.indices, grid.first().indices).map { runBFS(grid, it) }.max() ?: 0
}