Solution 2017-13 (Packet Scanners)

Author: rhaendel

src/main/kotlin/de/ronny_h/aoc/year2017/day13/PacketScanners.kt

@@ -0,0 +1,40 @@
+package de.ronny_h.aoc.year2017.day13
+
+import de.ronny_h.aoc.AdventOfCode
+
+fun main() = PacketScanners().run(1612, 3907994)
+
+class PacketScanners : AdventOfCode<Int>(2017, 13) {
+    override fun part1(input: List<String>): Int = input
+        .parseFirewallConfig()
+        .sumOf(::severity)
+
+    private fun severity(layer: ScanningArea): Int =
+        if (layer.isScannerOnTopInPicosecond(layer.depth)) {
+            layer.severity()
+        } else {
+            0
+        }
+
+    override fun part2(input: List<String>): Int {
+        val config = input
+            .parseFirewallConfig()
+
+        return generateSequence(0) { it + 1 }
+            .map { delay ->
+                delay to config.any { it.isScannerOnTopInPicosecond(it.depth + delay) }
+            }
+            .first { !it.second }
+            .first
+    }
+}
+
+data class ScanningArea(val depth: Int, val range: Int) {
+    fun isScannerOnTopInPicosecond(ps: Int): Boolean = ps % ((range - 1) * 2) == 0
+    fun severity() = depth * range
+}
+
+fun List<String>.parseFirewallConfig() = map {
+    val (depth, range) = it.split(": ")
+    ScanningArea(depth.toInt(), range.toInt())
+}

src/test/kotlin/de/ronny_h/aoc/year2017/day13/PacketScannersTest.kt

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+package de.ronny_h.aoc.year2017.day13
+
+import de.ronny_h.aoc.extensions.asList
+import io.kotest.core.spec.style.StringSpec
+import io.kotest.data.forAll
+import io.kotest.data.row
+import io.kotest.matchers.shouldBe
+
+class PacketScannersTest : StringSpec({
+
+    val input = """
+        0: 3
+        1: 2
+        4: 4
+        6: 4
+    """.asList()
+
+    "input can be parsed" {
+        input.parseFirewallConfig() shouldBe listOf(
+            ScanningArea(0, 3),
+            ScanningArea(1, 2),
+            ScanningArea(4, 4),
+            ScanningArea(6, 4),
+        )
+    }
+
+    "scanner is on top of the layer in the specific picosecond" {
+        forAll(
+            row(ScanningArea(0, 3), 0, true),
+            row(ScanningArea(1, 2), 0, true),
+            row(ScanningArea(4, 4), 0, true),
+            row(ScanningArea(6, 4), 0, true),
+            row(ScanningArea(0, 3), 1, false),
+            row(ScanningArea(1, 2), 1, false),
+            row(ScanningArea(4, 4), 1, false),
+            row(ScanningArea(6, 4), 1, false),
+            row(ScanningArea(0, 3), 2, false),
+            row(ScanningArea(1, 2), 2, true),
+            row(ScanningArea(4, 4), 2, false),
+            row(ScanningArea(6, 4), 2, false),
+            row(ScanningArea(0, 3), 3, false),
+            row(ScanningArea(1, 2), 3, false),
+            row(ScanningArea(4, 4), 3, false),
+            row(ScanningArea(6, 4), 3, false),
+            row(ScanningArea(0, 3), 4, true),
+            row(ScanningArea(1, 2), 4, true),
+            row(ScanningArea(4, 4), 4, false),
+            row(ScanningArea(6, 4), 4, false),
+        ) { layer, ps, expected ->
+            layer.isScannerOnTopInPicosecond(ps) shouldBe expected
+        }
+    }
+
+    "part 1: the severity of the example trip" {
+        PacketScanners().part1(input) shouldBe 24
+    }
+
+    "part 2: the fewest number of picoseconds to delay to get through safely" {
+        PacketScanners().part2(input) shouldBe 10
+    }
+})