Day04

Author: ath0s

src/main/kotlin/Day04.kt

@@ -0,0 +1,46 @@
+class Day04 : Day {
+    override fun partOne(filename: String, verbose: Boolean): Any {
+        val diagram = filename.asPath().parseMatrix()
+
+        val reachableCoordinates = mutableSetOf<Coordinate>()
+        diagram.forEachIndexed { coordinate, char ->
+            val neighbors = diagram.getAllNeighbors(coordinate)
+            val reachable = neighbors.count { diagram[it] == '@' } < 4
+            if (char == '@' && reachable) {
+                reachableCoordinates += coordinate
+            }
+        }
+
+        if (verbose) {
+            diagram.print { it in reachableCoordinates }
+        }
+        return reachableCoordinates.count()
+    }
+
+    override fun partTwo(filename: String, verbose: Boolean): Any {
+        val diagram = filename.asPath().parseMatrix()
+        val removed = mutableSetOf<Coordinate>()
+        do {
+            var changed = false
+            diagram.forEachIndexed { coordinate, char ->
+                val neighbors = diagram.getAllNeighbors(coordinate)
+                val reachable = neighbors.count { diagram[it] == '@' } < 4
+                if (char == '@' && reachable) {
+                    diagram[coordinate] = '.'
+                    removed += coordinate
+                    changed = true
+                }
+            }
+        } while (changed)
+
+        if (verbose) {
+            diagram.print { it in removed }
+        }
+        return removed.count()
+    }
+
+    companion object : Day.Main("Day04.txt") {
+        @JvmStatic
+        fun main(args: Array<String>) = main()
+    }
+}