First try to find a Christmas tree configuration: search for symmetries

Author: rhaendel

src/main/kotlin/Day14.kt

@@ -1,3 +1,5 @@
+import de.ronny_h.extensions.isSymmetrical
+
 fun main() {
     val day = "Day14"
 
@@ -10,7 +12,7 @@ fun main() {
         Robot(px.toInt(), py.toInt(), vx.toInt(), vy.toInt())
     }
 
-    fun List<Robot>.move(width: Int, height: Int, seconds: Int) = map {
+    fun List<Robot>.move(width: Int, height: Int, seconds: Long) = map {
         it.copy(
             px = (it.px + seconds * it.vx).mod(width),
             py = (it.py + seconds * it.vy).mod(height),
@@ -97,6 +99,55 @@ fun main() {
 
     val input = readInput(day)
     printAndCheck(input, ::part1, 218433348)
+
+
+    println("$day part 2")
+
+    fun List<Robot>.isNotSymmetrical(width: Int, height: Int): Boolean {
+        val grid = toGrid(width, height)
+        val symmetrical = grid.all { row ->
+            row.isSymmetrical()
+        }
+        if (symmetrical) {
+            grid.print()
+        }
+        return !symmetrical
+    }
+
+    fun iterateUntilSymmetrical(robots: List<Robot>, width: Int, height: Int): Long {
+        var seconds = 0L
+        do {
+            seconds++
+            if (seconds % 10000 == 0L) print('.')
+            if (seconds % 1000000 == 0L) println()
+            val result = robots.move(width, height, seconds)
+        } while (result.isNotSymmetrical(width, height))
+        return seconds
+    }
+
+    fun part2Small(input: List<String>) = iterateUntilSymmetrical(input.parseRobots(), 11, 7)
+
+    fun part2(input: List<String>) = iterateUntilSymmetrical(input.parseRobots(), 101, 103)
+
+    printAndCheck(
+        """
+            p=0,4 v=3,-3
+            p=6,3 v=-1,-3
+            p=10,3 v=-1,2
+            p=2,0 v=2,-1
+            p=0,0 v=1,3
+            p=3,0 v=-2,-2
+            p=7,6 v=-1,-3
+            p=3,0 v=-1,-2
+            p=9,3 v=2,3
+            p=7,3 v=-1,2
+            p=2,4 v=2,-3
+            p=9,5 v=-3,-3
+        """.trimIndent().lines(),
+        ::part2Small, 2
+    )
+
+    printAndCheck(input, ::part2, 91649162)
 }
 
 data class Robot(val px: Int, val py: Int, val vx: Int, val vy: Int)