day 16 (quicker solution for part one)

kgeri · Dec 20, 2022 · cd12ca0 · cd12ca0
1 parent d63a309
commit cd12ca0
Showing 1 changed file with 28 additions and 89 deletions.
diff --git a/src/main/kotlin/me/gergo/Aoc16.kt b/src/main/kotlin/me/gergo/Aoc16.kt
@@ -1,117 +1,56 @@
 package me.gergo
 
 import java.io.File
-import kotlin.math.max
+
+// TIL:
+// - Modeling these branching / optimization problems is MUCH more readable and faster when done with state -> newState Sets (rather than DFS / 
+//   recursive functions), and it also allows one to log the state space complexity easily
 
 fun main() {
     val valves = File("src/main/resources/input16.txt").readLines()
         .mapIndexed(::parseValves)
     val valvesByName = valves.associateBy(Valve::name)
     val neighbors = valves.associateWith { v -> v.tunnelsTo.map { valvesByName[it]!! } }
 
-    // Part One - dynamic programming, memoization
-    data class MemoKey(val valve: Valve, val opened: Set<Valve>, val minute: Int)
-
-    val memo = mutableMapOf<MemoKey, Int>()
-
-    fun findMaxPressure(current: Valve, opened: Set<Valve>, minute: Int): Int {
-        val key = MemoKey(current, opened, minute)
-        var max = memo[key]
-        if (max == null) {
-            val pressureReleased = opened.sumOf(Valve::rate)
-            max = pressureReleased + if (minute == 30) 0
-            else {
-                max(
-                    if (current.rate > 0 && !opened.contains(current)) // Stay here and open current valve (if the valve is not damaged)
-                        findMaxPressure(current, opened.plus(current), minute + 1) else 0,
-                    neighbors[current]!!.maxOf { // ...or don't open the valve and move to a neighbor
-                        findMaxPressure(it, opened, minute + 1)
-                    }
-                )
-            }
-            memo[key] = max
-        }
-        return max
-    }
-
     // FUK. I spent HOURS wondering why the sample data passes and my puzzle input does not... "You start at valve AA", NOT the first valve :|
     val aa = valves.first { it.name == "AA" }
 
-    val result1 = findMaxPressure(aa, emptySet(), 1)
-    println("Max pressure released : $result1")
-
-    // Part Two
-    data class MemoKey2(
-        val me: Valve,
-        val eli: Valve,
-        val opened: Long,
-        val openedRate: Int,
-        val meVisited: Long,
-        val eliVisited: Long,
-        val minute: Int
-    ) {
-        fun meCanOpen() = me.rate > 0 && !opened.isBitSet(me.index)
-        fun eliCanOpen() = eli.rate > 0 && !opened.isBitSet(eli.index)
-
-        fun meNeighbors() = neighbors[me]!!
-        fun eliNeighbors() = neighbors[eli]!!
-
-        fun meMovesEliOpens(neighbor: Valve) =
-            MemoKey2(neighbor, eli, opened.setBit(eli.index), openedRate + eli.rate, meVisited.setBit(me.index), eliVisited, minute + 1)
-
-        fun eliMovesMeOpens(neighbor: Valve) =
-            MemoKey2(me, neighbor, opened.setBit(me.index), openedRate + me.rate, meVisited, eliVisited.setBit(eli.index), minute + 1)
+    // Part One
+    var states = setOf(ValveState(aa, emptySet(), 0))
+    for (i in 1..30) {
 
-        fun weBothOpen() =
-            MemoKey2(me, eli, opened.setBit(me.index).setBit(eli.index), openedRate + me.rate + eli.rate, meVisited, eliVisited, minute + 1)
-
-        fun weBothMove(n1: Valve, n2: Valve) =
-            MemoKey2(n1, n2, opened, openedRate, meVisited.setBit(me.index), eliVisited.setBit(eli.index), minute + 1)
-    }
-
-    val memo2 = mutableMapOf<MemoKey2, Int>()
-
-    fun permutations(k: MemoKey2) = sequence {
-        if (k.meCanOpen() && k.eliCanOpen() && k.me != k.eli) yield(k.weBothOpen()) // Both valves can be opened
-        if (k.meCanOpen())
-            for (n in k.eliNeighbors()) { // My valve can be opened, Eli can move
-                if (k.meVisited.isBitSet(n.index)) continue // Eli shouldn't go where I went
-                yield(k.eliMovesMeOpens(n))
-            }
-        if (k.eliCanOpen())
-            for (n in k.meNeighbors()) { // Eli's valve can be opened, I can move
-                if (k.eliVisited.isBitSet(n.index)) continue // I shouldn't go where Eli went
-                yield(k.meMovesEliOpens(n))
-            }
-        for (mn in k.meNeighbors()) { // We both move
-            if (k.eliVisited.isBitSet(mn.index)) continue // I shouldn't go where Eli went
-            for (en in k.eliNeighbors()) {
-                if (k.meVisited.isBitSet(en.index)) continue // Eli shouldn't go where I went
-                yield(k.weBothMove(mn, en))
+        val newStates = HashSet<ValveState>(states.size * 2)
+        for (state in states) {
+            if (state.shouldOpen()) newStates.add(state.open())
+            for (n in neighbors[state.atValve]!!) {
+                newStates.add(state.moveTo(n))
             }
         }
+        println("Minute: $i, states: ${newStates.size}")
+        states = newStates
     }
 
-    fun findMaxPressureWithElephant(key: MemoKey2): Int {
-        if (key.minute == 26) return key.openedRate // We're done!
+    val result1 = states.maxOf { it.totalPressureReleased }
+    println("Max pressure released: $result1")
+}
 
-        val cachedMax = memo2[key]
-        if (cachedMax != null) return cachedMax
+private data class ValveState(val atValve: Valve, val opened: Set<Valve>, val totalPressureReleased: Int) {
 
-        val max = key.openedRate + (permutations(key).map(::findMaxPressureWithElephant).maxOrNull() ?: 0)
-        memo2[key] = max
+    fun moveTo(v: Valve): ValveState {
+        val pressureReleased = opened.sumOf(Valve::rate)
+        return ValveState(v, opened, totalPressureReleased + pressureReleased)
+    }
 
-        if (memo2.size % 1000000 == 0) println("Memo entries: ${memo2.size}")
-        return max
+    fun shouldOpen(): Boolean {
+        return atValve.rate > 0 && !opened.contains(atValve)
     }
 
-    val result2 = findMaxPressureWithElephant(MemoKey2(aa, aa, 0L, 0, 0L, 0L, 1))
-    println("Max pressure released with Eli: $result2")
+    fun open(): ValveState {
+        val pressureReleased = opened.sumOf(Valve::rate)
+        return ValveState(atValve, opened.plus(atValve), totalPressureReleased + pressureReleased)
+    }
 }
 
-private fun Long.isBitSet(index: Int): Boolean = this and (1L shl index) != 0L
-private fun Long.setBit(index: Int): Long = this or (1L shl index)
-
 private data class Valve(val index: Int, val name: String, val rate: Int, val tunnelsTo: List<String>)
 
 private val ValveTunnelFormat = Regex("Valve (\\w+) has flow rate=(\\d+); tunnels? leads? to valves? (.*)")