Day09 - Part 2

Author: ath0s

src/main/kotlin/Day09.kt

@@ -4,7 +4,7 @@ class Day09 : Day {
     override fun partOne(filename: String, verbose: Boolean): Long {
         val redTiles = filename.asPath().readLines().map {
             val (x, y) = it.split(",")
-            Coordinate(x.toInt(), y.toInt())
+            LongCoordinate(x.toLong(), y.toLong())
         }
         if (verbose) {
             val minX = redTiles.minOf { it.x }
@@ -14,7 +14,7 @@ class Day09 : Day {
 
             (minY..maxY).forEach { y ->
                 (minX..maxX).forEach { x ->
-                    if (Coordinate(x, y) in redTiles) {
+                    if (LongCoordinate(x, y) in redTiles) {
                         print('#')
                     } else {
                         print('.')
@@ -27,9 +27,8 @@ class Day09 : Day {
 
         redTiles.forEachIndexed { index, firstTile ->
             redTiles.drop(index + 1).forEach { secondTile ->
-                val ySize = maxOf(firstTile.y, secondTile.y) - minOf(firstTile.y, secondTile.y) + 1
-                val xSize = maxOf(firstTile.x, secondTile.x) - minOf(firstTile.x, secondTile.x) + 1
-                val size = ySize.toLong() * xSize.toLong()
+                val rectangle = Rectangle(firstTile, secondTile)
+                val size = rectangle.size
                 if (size > largestRectangle) {
                     largestRectangle = size
                 }
@@ -38,8 +37,47 @@ class Day09 : Day {
         return largestRectangle
     }
 
-    override fun partTwo(filename: String, verbose: Boolean): Any {
-        TODO("Not yet implemented")
+    override fun partTwo(filename: String, verbose: Boolean): Long {
+        val redTiles = filename.asPath().readLines().map {
+            val (x, y) = it.split(",")
+            LongCoordinate(x.toLong(), y.toLong())
+        }
+
+        val lines = redTiles.mapIndexed { index, a ->
+            Line(a, redTiles[(index + 1) % redTiles.size])
+        }
+
+        var max = 0L
+        redTiles.forEachIndexed { index, firstTile ->
+            var localMax = 0L
+            redTiles.drop(index + 1).forEach { secondTile ->
+                val probe = Rectangle(firstTile, secondTile).size
+                if (probe > localMax) {
+                    if (lines.none { it intersects Line(firstTile, secondTile) }) {
+                        localMax = probe
+                    }
+                }
+            }
+            max = maxOf(max, localMax)
+        }
+        return max
+    }
+
+    private infix fun Line.intersects(line2: Line): Boolean {
+        return line2.maxX > minX && line2.minX < maxX && line2.maxY > minY && line2.minY < maxY
+    }
+
+    private data class Line(val a: LongCoordinate, val b: LongCoordinate) {
+        val minX = minOf(a.x, b.x)
+        val maxX = maxOf(a.x, b.x)
+        val minY = minOf(a.y, b.y)
+        val maxY = maxOf(a.y, b.y)
+    }
+
+    private data class Rectangle(val a: LongCoordinate, val b: LongCoordinate) {
+        val width = maxOf(a.x, b.x) - minOf(a.x, b.x)
+        val height = maxOf(a.y, b.y) - minOf(a.y, b.y)
+        val size = (width + 1) * (height + 1)
     }
 
     companion object : Day.Main("Day09.txt") {

src/test/kotlin/Day09Test.kt

@@ -1,4 +1,4 @@
 class Day09Test : DayTest<Day09>("Day09_test.txt") {
     override val partOneExpected = 50L
-    override val partTwoExpected = null
+    override val partTwoExpected = 24L
 }