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solutions/day16/day16.go

@@ -0,0 +1,185 @@
+package day16
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+	"strings"
+	"unicode"
+)
+
+type Valve struct {
+	flowRate int
+	leadsTo  []string
+}
+
+type SimulationPoint struct {
+	time       int
+	imAt       string
+	elephantAt string
+	opened     string
+}
+
+type MovePair struct {
+	me       string
+	elephant string
+}
+
+func newMovePair(useElephant bool, a string, b string) MovePair {
+	if useElephant && a != "**" && b != "**" && b < a {
+		return MovePair{b, a}
+	} else {
+		return MovePair{a, b}
+	}
+}
+
+func addMovePair(pair MovePair, list *[]MovePair) {
+	for _, existing := range *list {
+		if existing.me == pair.me && existing.elephant == pair.elephant {
+			return
+		}
+	}
+	*list = append(*list, pair)
+}
+
+func alreadyVisited(place string, point SimulationPoint) bool {
+	for i := 0; i < len(point.opened); i += 2 {
+		if place[0] == point.opened[i] && place[1] == point.opened[i+1] {
+			return true
+		}
+	}
+	return false
+}
+
+func addPlace(place string, opened string) string {
+	injectionPoint := 0
+
+	for injectionPoint < len(opened) && (opened[injectionPoint] < place[0] || (opened[injectionPoint] == place[0] && opened[injectionPoint+1] < place[1])) {
+		injectionPoint += 2
+	}
+
+	return opened[0:injectionPoint] + place + opened[injectionPoint:]
+}
+
+var everythingOpened string
+var simulatedItems map[SimulationPoint]int
+
+func runSimulations(useElephant bool, time int, myPlace string, elephantAt string, opened string, valves map[string]Valve) int {
+	maxTime := 30
+	if useElephant {
+		maxTime = 26
+	}
+
+	if time == maxTime || everythingOpened == opened {
+		return 0
+	}
+
+	point := SimulationPoint{time, myPlace, elephantAt, opened}
+
+	if previousValue, ok := simulatedItems[point]; ok {
+		return previousValue
+	}
+
+	bestResult := 0
+
+	myMoves := []string{}
+	if !alreadyVisited(myPlace, point) && valves[myPlace].flowRate != 0 {
+		myMoves = append(myMoves, "**")
+	}
+	myMoves = append(myMoves, valves[myPlace].leadsTo...)
+
+	elephantMoves := []string{"AA"}
+	if useElephant {
+		elephantMoves = []string{}
+		if !alreadyVisited(elephantAt, point) && valves[elephantAt].flowRate != 0 && myPlace != elephantAt {
+			elephantMoves = append(elephantMoves, "**")
+		}
+		elephantMoves = append(elephantMoves, valves[elephantAt].leadsTo...)
+	}
+
+	moves := []MovePair{}
+	for _, myMove := range myMoves {
+		for _, elephantMove := range elephantMoves {
+			pair := newMovePair(useElephant, myMove, elephantMove)
+			addMovePair(pair, &moves)
+		}
+	}
+
+	for _, pair := range moves {
+		myMove := pair.me
+		elephantMove := pair.elephant
+		openReleases := 0
+		myNext := myPlace
+		elephantNext := elephantAt
+		nowOpen := opened
+
+		if myMove == "**" {
+			openReleases += valves[myPlace].flowRate * (maxTime - (time + 1))
+			nowOpen = addPlace(myPlace, nowOpen)
+		} else {
+			myNext = myMove
+		}
+
+		if elephantMove == "**" {
+			openReleases += valves[elephantAt].flowRate * (maxTime - (time + 1))
+			nowOpen = addPlace(elephantAt, nowOpen)
+		} else {
+			elephantNext = elephantMove
+		}
+
+		candidate := openReleases + runSimulations(useElephant, time+1, myNext, elephantNext, nowOpen, valves)
+		if candidate > bestResult {
+			bestResult = candidate
+		}
+	}
+
+	simulatedItems[point] = bestResult
+
+	return bestResult
+}
+
+func Run(filename string) {
+	file, err := os.Open(filename)
+
+	if err != nil {
+		fmt.Println("Error opening file:", err)
+		return
+	}
+
+	scanner := bufio.NewScanner(file)
+	scanner.Split(bufio.ScanLines)
+	valveMap := map[string]Valve{}
+	everythingOpened = ""
+
+	for scanner.Scan() {
+		line := scanner.Text()
+		var valve string
+		var rate int
+		fmt.Sscanf(line, "Valve %s has flow rate=%d", &valve, &rate)
+		_, after_semi, found_semi := strings.Cut(line, ";")
+		if !found_semi {
+			fmt.Println("PANIC: Couldn't find semi colon in line.")
+			return
+		}
+		after_semi = strings.TrimLeftFunc(after_semi, func(r rune) bool {
+			return !unicode.IsUpper(r)
+		})
+		targets := strings.Split(after_semi, ", ")
+
+		if rate > 0 {
+			everythingOpened = addPlace(valve, everythingOpened)
+		}
+
+		valveMap[valve] = Valve{rate, targets}
+	}
+
+	simulatedItems = map[SimulationPoint]int{}
+	bestRelease1 := runSimulations(false, 0, "AA", "AA", "", valveMap)
+	fmt.Println("Working on my own, best pressure release found is", bestRelease1)
+
+	simulatedItems = map[SimulationPoint]int{}
+	bestRelease2 := runSimulations(true, 0, "AA", "AA", "", valveMap)
+	fmt.Println("Working with an elephant, best pressure release found is", bestRelease2)
+
+	file.Close()
+}