From 8115b1c8ae674442ddd3069e1496abb7c7dc1747 Mon Sep 17 00:00:00 2001
From: Chris Hodges <chrishod@axis.com>
Date: Tue, 19 Dec 2023 15:28:31 +0100
Subject: [PATCH] Solved Part 2.

Change-Id: I5c3cab0446cb4761f9f6b97cc111b132da168475
---
 src/aoc2023/Day19.kt | 119 ++++++++++++++++++-------------------------
 1 file changed, 50 insertions(+), 69 deletions(-)

diff --git a/src/aoc2023/Day19.kt b/src/aoc2023/Day19.kt
index 9f98c0a..c42edde 100644
--- a/src/aoc2023/Day19.kt
+++ b/src/aoc2023/Day19.kt
@@ -78,7 +78,7 @@ hdj{m>838:A,pv}
 
     data class RuleCondition(val attr: Int = 0, val isSmaller: Boolean = false, val value: Int = 0, val follow: String)
 
-    fun part1(input: List<String>): Int {
+    fun createMap(input: List<String>): Pair<Int, Map<String, List<RuleCondition>>> {
         val ruleMap = HashMap<String, List<RuleCondition>>()
         var p = 0
         do {
@@ -102,10 +102,16 @@ hdj{m>838:A,pv}
             if (input[p].isBlank()) break
             p++
         } while (true)
+        return p to ruleMap
+    }
 
+    fun part1(input: List<String>): Int {
+        val (p, ruleMap) = createMap(input)
         var sum = 0
         for (pp in p + 1 until input.size) {
-            val attrs = input[pp].split("=", ",", "x", "m", "a", "s", "{", "}").filter { it.isNotBlank() }.map { it.toInt() }.toIntArray()
+            val attrs =
+                input[pp].split("=", ",", "x", "m", "a", "s", "{", "}").filter { it.isNotBlank() }.map { it.toInt() }
+                    .toIntArray()
             var ruleId = "in"
             while (ruleId != "A" && ruleId != "R") {
                 val conditions = ruleMap[ruleId]!!
@@ -130,74 +136,49 @@ hdj{m>838:A,pv}
         return sum
     }
 
-    fun part2(input: List<String>): Long {
-        val ruleMap = HashMap<String, List<RuleCondition>>()
-        var p = 0
-        do {
-            "([a-z]+)\\{(.*)}".toRegex().matchEntire(input[p])?.destructured
-                ?.let { (id, rules) ->
-                    val rulesList = rules.split(",").map {
-                        if (it.contains("<")) {
-                            val (attr, rest) = it.split("<")
-                            val (value, branchId) = rest.split(":")
-                            RuleCondition("xmas".indexOf(attr), true, value.toInt(), branchId)
-                        } else if (it.contains(">")) {
-                            val (attr, rest) = it.split(">")
-                            val (value, branchId) = rest.split(":")
-                            RuleCondition("xmas".indexOf(attr), false, value.toInt(), branchId)
-                        } else {
-                            RuleCondition(follow = it)
-                        }
-                    }
-                    ruleMap[id] = rulesList
-                }
-            if (input[p].isBlank()) break
-            p++
-        } while (true)
-        var prod = 1L
-        for (attridx in 0..3) {
-            var numaccept = 0
-            for (attrvalue in 1..4000) {
-                val destRules = HashSet<String>()
-                val destRulesWithCond = HashSet<String>()
-                val ruleQueue = ArrayDeque<String>()
-                val ruleWithCondQueue = ArrayDeque<String>()
-                ruleQueue.add("in")
-                var rejected = false
-                while (ruleQueue.isNotEmpty()) {
-                    val ruleId = ruleQueue.removeFirst()
-                    if (ruleId == "R" || ruleId == "A") continue
-                    val conditions = ruleMap[ruleId]!!
-                    for (cond in conditions) {
-                        if (cond.value != 0 && cond.attr == attridx) {
-                            val accept = if (cond.isSmaller) {
-                                attrvalue < cond.value
-                            } else {
-                                attrvalue > cond.value
-                            }
-                            if (accept) {
-                                if (!destRulesWithCond.contains(cond.follow)) {
-                                    destRules.add(cond.follow)
-                                    destRulesWithCond.add(cond.follow)
-                                    ruleQueue.add(cond.follow)
-                                }
-                            }
-                        } else {
-                            if (!destRules.contains(cond.follow)) {
-                                destRules.add(cond.follow)
-                                ruleQueue.add(cond.follow)
-                            }
-                            if (destRulesWithCond.contains(ruleId)) {
-                                destRulesWithCond.add(cond.follow)
-                            }
-                        }
-                    }
-                }
-                if (destRulesWithCond.contains("A")) numaccept++
-            }
-            prod *= numaccept
+    fun recurse(ruleMap: Map<String, List<RuleCondition>>, ranges: List<IntRange>, ruleId: String): Long {
+        if (ruleId == "A") {
+            return ranges.map { (it.last - it.first + 1).coerceAtLeast(0).toLong() }.reduce(Long::times)
         }
-        return prod
+        if (ruleId == "R") return 0
+        var result = 0L
+        val conditions = ruleMap[ruleId]!!
+        var currRanges = ranges
+        for (cond in conditions) {
+            if (cond.value != 0) {
+                if (cond.isSmaller) {
+                    val subRange = currRanges.mapIndexed { index, intRange ->
+                        if (index != cond.attr) intRange else
+                            IntRange(intRange.first, intRange.last.coerceAtMost(cond.value - 1))
+                    }
+                    result += recurse(ruleMap, subRange, cond.follow)
+                    currRanges = currRanges.mapIndexed { index, intRange ->
+                        if (index != cond.attr) intRange else
+                            IntRange(intRange.first.coerceAtLeast(cond.value), intRange.last)
+                    }
+                } else {
+                    val subRange = currRanges.mapIndexed { index, intRange ->
+                        if (index != cond.attr) intRange else
+                            IntRange(intRange.first.coerceAtLeast(cond.value + 1), intRange.last)
+                    }
+                    result += recurse(ruleMap, subRange, cond.follow)
+                    currRanges = currRanges.mapIndexed { index, intRange ->
+                        if (index != cond.attr) intRange else
+                            IntRange(intRange.first, intRange.last.coerceAtMost(cond.value))
+                    }
+                }
+            } else {
+                result += recurse(ruleMap, currRanges, cond.follow)
+                break
+            }
+        }
+        return result
+    }
+
+    fun part2(input: List<String>): Long {
+        val (_, ruleMap) = createMap(input)
+        val ranges = listOf(IntRange(1, 4000), IntRange(1, 4000), IntRange(1, 4000), IntRange(1, 4000))
+        return recurse(ruleMap, ranges, "in")
     }
 
     // test if implementation meets criteria from the description, like: