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day 15 solution, part 1
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‎.idea/gradle.xml

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‎day15/build.gradle.kts

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plugins {
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id("org.adventofcode.kotlin-application-conventions")
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}
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dependencies {
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}
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application {
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mainClass.set("org.adventofcode.AppKt")
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}

‎day15/src/main/kotlin/org/adventofcode/App.kt

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package org.adventofcode
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import java.io.File
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data class Point(val col: Int, val row: Int)
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typealias Path = List<Point>
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fun Point.above(): Point = Point(col, row - 1)
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fun Point.below(): Point = Point(col, row + 1)
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fun Point.right(): Point = Point(col + 1, row)
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fun Point.left(): Point = Point(col - 1, row)
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fun Point.neighbors(): List<Point> = listOf(above(), below(), left(), right())
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fun Point.toCompactString(): String = "($col,$row)"
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val ORIGIN_POINT = Point(0, 0)
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interface Grid {
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val width: Int;
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val height: Int;
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val lastPoint: Point;
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operator fun contains(p: Point): Boolean;
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operator fun get(p: Point): Int?;
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}
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data class ImmutableGrid(val data: List<List<Int>>) : Grid {
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override val height: Int by lazy { data.size }
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override val width: Int by lazy { if (data.isNotEmpty()) data[0].size else 0 }
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override val lastPoint: Point by lazy { Point(width - 1, height -1 ) }
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override operator fun contains(p: Point): Boolean {
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val insideRowRange = p.row in 0 until height
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val insideColRange = p.col in 0 until width
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return insideRowRange && insideColRange
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}
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override fun get(p: Point): Int? {
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return data[p.row][p.col]
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}
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}
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fun ImmutableGrid.prettyPrint(withPath: Path? = null) {
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val pointset = withPath?.let { it.toSet() } ?: setOf()
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val padding = 2 + (withPath?.let { 4 } ?: 0)
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this.data.forEachIndexed { rowIdx, row ->
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val s = row.mapIndexed { colIdx, value ->
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val point = Point(colIdx, rowIdx)
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val attr = withPath?.let { if (point in pointset) "{*}" else null }
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"$value${attr?.let { it } ?: ""}".padEnd(padding)
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}
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println(s.joinToString(""))
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}
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}
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data class TraversalEntry(val parent: Point? = null, val cost: Double = 0.0)
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object PathFinder {
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fun findShortestPath(grid: Grid): Path {
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val destinationPoint = grid.lastPoint
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val initTraversalEntry = TraversalEntry()
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val traversedEntries = mutableMapOf(ORIGIN_POINT to initTraversalEntry)
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val openEntries = mutableListOf(ORIGIN_POINT to initTraversalEntry)
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while (openEntries.isNotEmpty()) {
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val (currentPoint, currentEntry) = openEntries.removeFirst()
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if (currentPoint == destinationPoint) {
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break
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}
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val neighboringPoints = currentPoint.neighbors().filter { p -> p in grid }
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for (neighborPoint in neighboringPoints) {
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val neighborValue = grid[neighborPoint] ?: throw error("Invalid neighboring point $neighborPoint")
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val nextCost = currentEntry.cost + neighborValue
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val neighborEntry = traversedEntries[neighborPoint]
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val entry = if ((neighborEntry == null) || (nextCost < neighborEntry.cost)) {
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TraversalEntry(parent = currentPoint, cost = nextCost)
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} else null
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entry?.let {
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openEntries.add(neighborPoint to it)
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traversedEntries[neighborPoint] = it
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}
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}
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openEntries.sortBy { (_, entry) -> entry.cost }
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}
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val destinationEntry = traversedEntries[destinationPoint]
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val pathSequence = generateSequence(destinationEntry) {
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traversedEntries[it.parent]
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}
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return pathSequence.toList().mapNotNull { it.parent }.reversed() + destinationPoint
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}
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}
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fun main() {
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val data = File("day15/src/main/resources/puzzleInput.txt")
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.readLines()
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.map { it.split("").drop(1).dropLast(1).map(String::toInt) }
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val grid = ImmutableGrid(data)
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val path = PathFinder.findShortestPath(grid)
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grid.prettyPrint(path)
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println()
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val cost = path.drop(1).sumOf { grid[it] ?: 0 }
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println("total cost: $cost")
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}

‎day15/src/main/resources/puzzleInput.txt

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100+
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‎day15/src/main/resources/sampleInput.txt

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1163751742
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1381373672
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2136511328
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3694931569
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7463417111
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1319128137
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1359912421
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3125421639
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1293138521
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2311944581

‎day15/src/main/resources/sampleInput2.txt

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19111
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19191
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11191
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99991
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99991

‎settings.gradle.kts

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"day12",
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"day13",
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"day14",
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"day15",
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)

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