Day12

days/src/main/kotlin/Day12.kt

@@ -0,0 +1,88 @@
+package be.vandewalleh.aoc.days
+
+import be.vandewalleh.aoc.utils.input.Day
+import be.vandewalleh.aoc.utils.input.Input
+import be.vandewalleh.aoc.utils.input.Lines
+import be.vandewalleh.aoc.utils.input.createDay
+import kotlin.math.abs
+
+@Day(12)
+class Day12(@Lines val input: Input<List<String>>) {
+
+    fun part1(): Int {
+        var x = 0
+        var y = 0
+        var facing = "E"
+
+        val dirs = listOf("N", "E", "S", "W")
+
+        input.value.forEach {
+            val dir = it.take(1)
+            val steps = it.drop(1).toInt()
+
+            when (dir) {
+                "L" -> repeat(steps / 90) {
+                    val i = (dirs.indexOf(facing) + 4 - 1) % 4
+                    facing = dirs[i]
+                }
+                "R" -> repeat(steps / 90) {
+                    val i = (dirs.indexOf(facing) + 1) % 4
+                    facing = dirs[i]
+                }
+            }
+
+            when (if (dir == "F") facing else dir) {
+                "N" -> y -= steps
+                "S" -> y += steps
+                "W" -> x -= steps
+                "E" -> x += steps
+            }
+
+        }
+
+        return abs(x) + abs(y)
+    }
+
+    fun part2(): Int {
+        var x = 0
+        var y = 0
+
+        var waypointX = 10
+        var waypointY = -1
+
+        input.value.forEach {
+            val dir = it.take(1)
+            val steps = it.drop(1).toInt()
+
+            when (dir) {
+                "L" -> repeat(steps / 90) {
+                    val oldY = waypointY
+                    waypointY = -waypointX
+                    waypointX = oldY
+                }
+                "R" -> repeat(steps / 90) {
+                    val oldY = waypointY
+                    waypointY = waypointX
+                    waypointX = -oldY
+                }
+            }
+            when (dir) {
+                "F" -> {
+                    x += waypointX * steps
+                    y += waypointY * steps
+                }
+                "N" -> waypointY -= steps
+                "S" -> waypointY += steps
+                "W" -> waypointX -= steps
+                "E" -> waypointX += steps
+            }
+        }
+
+        return abs(x) + abs(y)
+    }
+}
+
+fun main() = with(createDay<Day12>()) {
+    println(part1())
+    println(part2())
+}

days/src/main/resources/day12.txt

@@ -0,0 +1,770 @@
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