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import java.util.*
object Day15 {
private class CustomPriorityQueue<T>(private val array: Array<T>, private val comparator: Comparator<T>) {
init {
array.sortWith(comparator)
}
private var i = 0
private fun indexOfStartingFrom(elem: T, start: Int): Int {
for (i in (start until array.size)) {
if (array[i] == elem) {
return i
}
}
return -1
}
fun isNotEmpty(): Boolean = i < array.size
fun take(): T = array[i++]
fun revalidate(elem: T) {
val currentIndex = indexOfStartingFrom(elem, i)
if (currentIndex == -1) {
return
}
val newIndex = Arrays
.binarySearch(array, i, currentIndex, elem, comparator)
.let { if (it >= 0) it else -(it + 1) }
System.arraycopy(array, newIndex, array, newIndex + 1, currentIndex - newIndex)
array[newIndex] = elem
}
}
private class Matrix(private val data: Array<IntArray>, private val size: Int) {
companion object {
fun fromInput(input: List<String>): Matrix {
val data = input.map { line ->
line.map { it.digitToInt() }.toIntArray()
}.toTypedArray()
check(data.isNotEmpty()) { "No rows found!" }
check(data.first().isNotEmpty()) { "No columns found!" }
return Matrix(data, data.size)
}
}
fun expand(): Matrix {
val expandedData = Array(size * 5) { row ->
IntArray(size * 5) { col ->
((data[row % size][col % size] + row / size + col / size) - 1) % 9 + 1
}
}
return Matrix(expandedData, size * 5)
}
private fun neighbours(pos: Pair<Int, Int>): Sequence<Pair<Int, Int>> {
val offsets = sequenceOf(0 to 1, 1 to 0, 0 to -1, -1 to 0)
return offsets
.map { pos.first + it.first to pos.second + it.second }
.filter { it.first in 0 until size && it.second in 0 until size }
}
fun dijkstra(): Int {
val positions = (0 until size)
.flatMap { row -> (0 until size).map { col -> row to col } }
val distances =
positions
.associateWith { Int.MAX_VALUE }
.toMutableMap()
distances[0 to 0] = 0
val queue = CustomPriorityQueue(positions.toTypedArray(), compareBy { distances[it]!! })
while (queue.isNotEmpty()) {
val u = queue.take()
for (v in neighbours(u)) {
val newDist = distances[u]!! + data[v.first][v.second]
if (distances[v]!! > newDist) {
distances[v] = newDist
queue.revalidate(v)
}
}
}
return distances[size - 1 to size - 1]!!
}
}
fun part1(input: List<String>): Int = Matrix.fromInput(input).dijkstra()
fun part2(input: List<String>): Int = Matrix.fromInput(input).expand().dijkstra()
}
fun main() {
val testInput = readInputAsLines("Day15_test")
check(Day15.part1(testInput) == 40)
check(Day15.part2(testInput) == 315)
val input = readInputAsLines("Day15")
println(Day15.part1(input))
println(Day15.part2(input))
}
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