Part 1 at least.

src/aoc2023/Day22.kt

@@ -144,9 +144,13 @@ fun main() {
         override fun hashCode(): Int {
             return id
         }
+
+        override fun toString(): String {
+            return "Brick(id=$id, uponBricks=$uponBricks)"
+        }
     }
 
-    fun part1(input: List<String>, width: Int, height: Int): Int {
+    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!!
             Brick(id, x1.toInt(), y1.toInt(), z1.toInt(), x2.toInt(), y2.toInt(), z2.toInt())
@@ -175,30 +179,27 @@ fun main() {
                     brickTopZ[y * width + x] = flatTopZ + b.h()
                 }
             }
-            brickTopZ.asSequence().chunked(width).joinToString("\n") { it.joinToString(" ") { String.format("%3d", it) } }.println()
-            println()
+            //brickTopZ.asSequence().chunked(width).joinToString("\n") { it.joinToString(" ") { String.format("%3d", it) } }.println()
+            //println()
         }
-        val supportSuperSet = HashSet<Brick>()
-        bricks.forEach { if (it.onTopBricks.size != 1) supportSuperSet.addAll(it.onTopBricks) }
-        println(bricks.map { "%c: %d".format(('A' + it.id), it.onTopBricks.size) })
-        return bricks.count { it.uponBricks.size != 1 }
-    }
-
-    fun part2(input: List<String>): Int {
-        return 0
+        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
     }
 
     // test if implementation meets criteria from the description, like:
     val testInput = inlineTestInput.trim().reader().readLines()
     //val testInput = readInput("aoc2023/Day22_test")
-    val testInputPart1Result = part1(testInput, 3, 3)
+    val (testInputPart1Result, testInputPart2Result) = parts(testInput, 3, 3)
     println("Part 1 Test: $testInputPart1Result")
-    val testInputPart2Result = part2(testInput)
     println("Part 2 Test: $testInputPart2Result")
     check(testInputPart1Result == 5)
-    check(testInputPart2Result == 0)
+    check(testInputPart2Result == 7)
 
     val input = readInput("aoc2023/Day22")
-    part1(input, 10, 10).println()
-    part2(input).println()
+    parts(input, 10, 10).println()
 }