From 946048f3f190ce3f1aa58a741c85225a2d54fcca Mon Sep 17 00:00:00 2001
From: Chris Hodges <chrishod@axis.com>
Date: Fri, 22 Dec 2023 10:28:32 +0100
Subject: [PATCH] Day 22 Part 2.

Change-Id: I60222815834fd3180a842d3c0f1f70bc9ed2ed67
---
 src/aoc2023/Day22.kt | 24 ++++++++++++++++--------
 1 file changed, 16 insertions(+), 8 deletions(-)

diff --git a/src/aoc2023/Day22.kt b/src/aoc2023/Day22.kt
index f3f4aa6..5acee1f 100644
--- a/src/aoc2023/Day22.kt
+++ b/src/aoc2023/Day22.kt
@@ -152,7 +152,8 @@ fun main() {
 
     fun parts(input: List<String>, width: Int, height: Int): Pair<Int, Int> {
         val bricks = input.mapIndexed { id, it ->
-            val (x1, y1, z1, x2, y2, z2) = "(\\d+),(\\d+),(\\d+)~(\\d+),(\\d+),(\\d+)".toRegex().matchEntire(it)?.destructured!!
+            val (x1, y1, z1, x2, y2, z2) = "(\\d+),(\\d+),(\\d+)~(\\d+),(\\d+),(\\d+)".toRegex()
+                .matchEntire(it)?.destructured!!
             Brick(id, x1.toInt(), y1.toInt(), z1.toInt(), x2.toInt(), y2.toInt(), z2.toInt())
         }
             .sortedBy { it.z2 }
@@ -179,16 +180,23 @@ fun main() {
                     brickTopZ[y * width + x] = flatTopZ + b.h()
                 }
             }
-            //brickTopZ.asSequence().chunked(width).joinToString("\n") { it.joinToString(" ") { String.format("%3d", it) } }.println()
-            //println()
         }
-        val fallingSet = HashSet<Brick>()
-        //println(bricks.map { "%c: %d".format(('A' + it.id), it.onTopBricks.size) })
         val disBricks = bricks.filterNot { it.onTopBricks.all { it.uponBricks.size != 1 } }
         val safeBricks = bricks.size - disBricks.size
-        println(disBricks)
-        val fallingBricks = disBricks.map { it.onTopBricks.filter { it.uponBricks.size < 2 }.size }.sum()
-        return safeBricks to fallingBricks
+        var sum = 0
+        for (brick in disBricks) {
+            val fallingSet = HashSet<Brick>()
+            val removeQueue = ArrayDeque<Brick>()
+            fallingSet.add(brick)
+            removeQueue.add(brick)
+            while (removeQueue.isNotEmpty()) {
+                val falling = removeQueue.removeFirst()
+                fallingSet.add(falling)
+                removeQueue.addAll(falling.onTopBricks.filter { it.uponBricks.subtract(fallingSet).isEmpty() })
+            }
+            sum += fallingSet.size - 1
+        }
+        return safeBricks to sum
     }
 
     // test if implementation meets criteria from the description, like: