Solution 2018-11, part 1 (Chronal Charge)

Author: rhaendel

src/main/kotlin/de/ronny_h/aoc/year2018/day11/ChronalCharge.kt

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+package de.ronny_h.aoc.year2018.day11
+
+import de.ronny_h.aoc.AdventOfCode
+import de.ronny_h.aoc.extensions.grids.Grid
+import de.ronny_h.aoc.extensions.numbers.digit
+
+fun main() = ChronalCharge().run("34,13", "")
+
+class ChronalCharge : AdventOfCode<String>(2018, 11) {
+    // start:  11:59
+    override fun part1(input: List<String>): String {
+        val grid = PowerCellGrid(input.single().toInt())
+        return grid.find3x3SquareWithLargestTotal()
+    }
+
+    override fun part2(input: List<String>): String {
+        return ""
+    }
+}
+
+class PowerCellGrid(serialNumber: Int) : Grid<Int>(300, 300, -1000) {
+    init {
+        forEachIndex { y, x ->
+            val rackId = x + 10
+            var powerLevel = rackId * y + serialNumber
+            powerLevel *= rackId
+            val hundredsDigit = powerLevel.digit(3)
+            this[y, x] = hundredsDigit - 5
+        }.last()
+    }
+
+    fun find3x3SquareWithLargestTotal(): String {
+        val maxCoordinates = forEachCoordinates { coordinates, _ ->
+            val total = (0..2).sumOf { i ->
+                (0..2).sumOf { j ->
+                    this[coordinates.row + i, coordinates.col + j]
+                }
+            }
+            coordinates to total
+        }
+            .maxBy { it.second }
+            .first
+        return "${maxCoordinates.col},${maxCoordinates.row}"  // X,Y
+    }
+
+    override fun Char.toElementType(): Int = digitToInt()
+}

src/test/kotlin/de/ronny_h/aoc/year2018/day11/ChronalChargeTest.kt

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+package de.ronny_h.aoc.year2018.day11
+
+import io.kotest.core.spec.style.StringSpec
+import io.kotest.data.forAll
+import io.kotest.data.row
+import io.kotest.matchers.shouldBe
+
+class ChronalChargeTest : StringSpec({
+
+    "the power level of the fuel cell at coordinates in a grid with a given serial number" {
+        forAll(
+            row(3, 5, 8, 4),
+            row(122, 79, 57, -5),
+            row(217, 196, 39, 0),
+            row(101, 153, 71, 4),
+        ) { x, y, serialNumber, powerLevel ->
+            PowerCellGrid(serialNumber)[y, x] shouldBe powerLevel
+        }
+    }
+
+    "part 1: For grid serial number 18, the largest total 3x3 square has a top-left corner of 33,45" {
+        ChronalCharge().part1(listOf("18")) shouldBe "33,45"
+    }
+
+    "part 1: For grid serial number 42, the largest 3x3 square's top-left is 21,61" {
+        ChronalCharge().part1(listOf("42")) shouldBe "21,61"
+    }
+
+    "part 2" {
+        val input = listOf("")
+        ChronalCharge().part2(input) shouldBe ""
+    }
+})