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import kotlin.math.absoluteValue
import kotlin.math.max
import kotlin.math.sign
object Day05 {
private data class Line(val start: Pos2D, val end: Pos2D) {
companion object {
fun fromString(input: String): Line {
val (start, end) = input.split(" -> ").map { coordinateString ->
val (x, y) = coordinateString.split(",").map(String::toInt)
Pos2D(x, y)
}
return Line(start, end)
}
}
val isHorizontalOrVertical: Boolean
get() = start.x == end.x || start.y == end.y
val isDiagonal: Boolean
get() = (end.x - start.x).absoluteValue == (end.y - start.y).absoluteValue
val pointSequence: Sequence<Pos2D>
get() = sequence {
val xOffset = end.x - start.x
val yOffset = end.y - start.y
for (s in 0..max(xOffset.absoluteValue, yOffset.absoluteValue)) {
val x = start.x + s * xOffset.sign
val y = start.y + s * yOffset.sign
yield(Pos2D(x, y))
}
}
}
private fun helper(input: List<String>, linePredicate: (line: Line) -> Boolean) = input
.asSequence()
.map(Line::fromString)
.filter(linePredicate)
.flatMap(Line::pointSequence)
.groupingBy { it }
.eachCount()
.values
.count { it >= 2 }
fun part1(input: List<String>): Int = helper(input, Line::isHorizontalOrVertical)
fun part2(input: List<String>): Int = helper(input) { it.isHorizontalOrVertical || it.isDiagonal }
}
fun main() {
val testInput = readInputAsLines("Day05_test")
check(Day05.part1(testInput) == 5)
check(Day05.part2(testInput) == 12)
val input = readInputAsLines("Day05")
println(Day05.part1(input))
println(Day05.part2(input))
}
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