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object Day09 {
private fun Map<Pos2D, Int>.getLowPoints() =
filter { (pos, num) -> Pos2D.directions4.all { num < getOrDefault(pos + it, 9) } }
fun part1(input: List<String>) =
parseToMap(input).getLowPoints().values.sumOf { it + 1 }
fun part2(input: List<String>): Int {
val map = parseToMap(input)
fun traverseBasin(pos: Pos2D, acc: MutableSet<Pos2D>) {
acc.add(pos)
Pos2D.directions4
.map { pos + it }
.filter { !acc.contains(it) && map.getOrDefault(it, 9) < 9 }
.forEach { traverseBasin(it, acc) }
}
return map
.getLowPoints()
.map {
val visited = mutableSetOf<Pos2D>()
traverseBasin(it.key, visited)
visited.size
}
.sortedDescending()
.take(3)
.sum()
}
}
fun main() {
val testInput = readInputAsLines("Day09_test")
check(Day09.part1(testInput) == 15)
check(Day09.part2(testInput) == 1134)
val input = readInputAsLines("Day09")
println(Day09.part1(input))
println(Day09.part2(input))
}
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