Solution for 2023-12-11, part 1

src/main/kotlin/biz/koziolek/adventofcode/year2023/day11/day11.kt

@@ -0,0 +1,72 @@
+package biz.koziolek.adventofcode.year2023.day11
+
+import biz.koziolek.adventofcode.Coord
+import biz.koziolek.adventofcode.findInput
+
+fun main() {
+    val inputFile = findInput(object {})
+    val map = parseGalaxyMap(inputFile.bufferedReader().readLines())
+    println("Sum of shortest paths between every pair in expanded universe is: ${map.expand().distances.sum()}")
+}
+
+const val GALAXY = '#'
+const val VOID = '.'
+
+data class GalaxyMap(val galaxies: Set<Coord>) {
+    val width = galaxies.maxOf { it.x } + 1
+    val height = galaxies.maxOf { it.y } + 1
+    val distances: List<Int> by lazy {
+        val galaxiesList = galaxies.toList()
+        galaxiesList
+            .flatMapIndexed { firstIdx, firstCoord ->
+                galaxiesList
+                    .filterIndexed { secondIndex, _ -> secondIndex > firstIdx }
+                    .map { secondCoord -> firstCoord to secondCoord }
+            }
+            .map { it.first.manhattanDistanceTo(it.second) }
+    }
+
+    fun expand(): GalaxyMap {
+        val emptyColumns = (0..width) - galaxies.map { it.x }.toSet()
+        val emptyRows = (0..height) - galaxies.map { it.y }.toSet()
+
+        return GalaxyMap(
+            galaxies = galaxies.map { oldCoord ->
+                Coord(
+                    x = oldCoord.x + emptyColumns.count { it < oldCoord.x },
+                    y = oldCoord.y + emptyRows.count { it < oldCoord.y },
+                )
+            }.toSet(),
+        )
+    }
+
+    override fun toString() =
+        buildString {
+            for (y in 0 until height) {
+                for (x in 0 until width) {
+                    val coord = Coord(x, y)
+
+                    if (coord in galaxies) {
+                        append(GALAXY)
+                    } else {
+                        append(VOID)
+                    }
+                }
+
+                if (y != height - 1) {
+                    append("\n")
+                }
+            }
+        }
+}
+
+fun parseGalaxyMap(lines: Iterable<String>): GalaxyMap =
+    lines.flatMapIndexed { y, line ->
+        line.mapIndexedNotNull { x, char ->
+            if (char == GALAXY) {
+                Coord(x, y)
+            } else {
+                null
+            }
+        }
+    }.let { GalaxyMap(it.toSet()) }