Finish day 13

2 files changed, 105 insertions, 3 deletions

diff --git a/README.md b/README.md
index 7893928..991e42c 100644
--- a/README.md
+++ b/README.md
@@ -1,7 +1,7 @@
 # Advent of Code 2021 in Kotlin
 ![Kotlin](https://img.shields.io/badge/Kotlin-grey?logo=Kotlin)
-![](https://img.shields.io/badge/⭐%20stars-28-yellow)
-![](https://img.shields.io/badge/📅%20days-14-blue)
+![](https://img.shields.io/badge/⭐%20stars-30-yellow)
+![](https://img.shields.io/badge/📅%20days-15-blue)
 
 Welcome to the Advent of Code[^aoc] Kotlin project created by [tchojnacki][github] using the [Advent of Code Kotlin Template][template] delivered by JetBrains.
 
@@ -20,7 +20,7 @@ Welcome to the Advent of Code[^aoc] Kotlin project created by [tchojnacki][githu
 | Day 10: Syntax Scoring          |   🌟   |   🌟   |
 | Day 11: Dumbo Octopus           |   🌟   |   🌟   |
 | Day 12: Passage Pathing         |   🌟   |   🌟   |
-| Day 13: Transparent Origami     |        |        |
+| Day 13: Transparent Origami     |   🌟   |   🌟   |
 | Day 14: Extended Polymerization |   🌟   |   🌟   |
 | Day 15: Chiton                  |   🌟   |   🌟   |
 | Day 16: Packet Decoder          |        |        |
diff --git a/src/Day13.kt b/src/Day13.kt
new file mode 100644
index 0000000..f37c527
--- /dev/null
+++ b/src/Day13.kt
@@ -0,0 +1,102 @@
+import java.lang.IllegalStateException
+
+sealed class FoldCommand {
+    abstract fun dispatch(dots: Set<Pos2D>): Set<Pos2D>
+
+    class AlongX(private val x: Int) : FoldCommand() {
+        override fun dispatch(dots: Set<Pos2D>): Set<Pos2D> = dots
+            .filter { it.x != x }
+            .map {
+                if (it.x < x) {
+                    it
+                } else {
+                    Pos2D(2 * x - it.x, it.y)
+                }
+            }
+            .toSet()
+    }
+
+    class AlongY(val y: Int) : FoldCommand() {
+        override fun dispatch(dots: Set<Pos2D>): Set<Pos2D> = dots
+            .filter { it.y != y }
+            .map {
+                if (it.y < y) {
+                    it
+                } else {
+                    Pos2D(it.x, 2 * y - it.y)
+                }
+            }
+            .toSet()
+    }
+}
+
+fun parseOrigami(input: List<String>): Pair<Set<Pos2D>, Sequence<FoldCommand>> {
+    val dots = mutableSetOf<Pos2D>()
+    val commands = mutableListOf<FoldCommand>()
+
+    for (line in input) {
+        if (line.matches("\\d+,\\d+".toRegex())) {
+            val (x, y) = line.split(",").map(String::toInt)
+            dots.add(Pos2D(x, y))
+        }
+
+        if (line.matches("fold along [xy]=\\d+".toRegex())) {
+            val equation = line.substring(11)
+            val (axis, valueString) = equation.split("=")
+            val value = valueString.toInt()
+
+            commands.add(
+                when (axis) {
+                    "x" -> FoldCommand.AlongX(value)
+                    "y" -> FoldCommand.AlongY(value)
+                    else -> throw IllegalStateException("Illegal axis given!")
+                }
+            )
+        }
+    }
+
+    return dots to commands.asSequence()
+}
+
+fun main() {
+    fun part1(input: List<String>): Int {
+        val (dots, commands) = parseOrigami(input)
+
+        val res = commands.first().dispatch(dots).size
+
+        return res
+    }
+
+    fun part2(input: List<String>): String {
+        val origami = parseOrigami(input)
+        var dots = origami.first
+        val commands = origami.second
+
+        commands.forEach {
+            dots = it.dispatch(dots)
+        }
+
+        val bounds = dots.reduce { max, pos ->
+            when ((pos.x > max.x) to (pos.y > max.y)) {
+                true to true -> pos
+                true to false -> Pos2D(pos.x, max.y)
+                false to true -> Pos2D(max.x, pos.y)
+                else -> max
+            }
+        }
+
+        val lines = Array(bounds.y + 1) { Array(bounds.x + 1) { ' ' } }
+
+        dots.forEach { lines[it.y][it.x] = '#' }
+
+        return lines.joinToString("\n") { it.joinToString("") }
+    }
+
+
+    val testInput = readInputAsLines("Day13_test")
+    check(part1(testInput) == 17)
+
+    val input = readInputAsLines("Day13")
+    println(part1(input))
+    println(part2(input))
+}