feat: solve part one using brute-force permutation search

internal/2015/DayThirteen/code.go

@@ -0,0 +1,114 @@
+package daythirteen
+
+import (
+	"advent-of-code/internal/registry"
+	"math"
+	"os"
+	"regexp"
+	"strconv"
+	"strings"
+)
+
+var inputPattern = regexp.MustCompile(`(\w+) would (gain|lose) (\d+) happiness units by sitting next to (\w+)\.?`)
+
+func init() {
+	registry.Register("2015D13", ParseInput, PartOne, PartTwo)
+}
+
+func buildHappinessMap(data []string) map[string]map[string]int {
+	happinessMap := make(map[string]map[string]int)
+
+	for _, line := range data {
+		matches := inputPattern.FindStringSubmatch(line)
+		person := matches[1]
+		operation := matches[2]
+		value, _ := strconv.Atoi(matches[3])
+		neighbor := matches[4]
+
+		if happinessMap[person] == nil {
+			happinessMap[person] = make(map[string]int)
+		}
+
+		if operation == "gain" {
+			happinessMap[person][neighbor] = value
+		} else {
+			happinessMap[person][neighbor] = -value
+		}
+	}
+
+	return happinessMap
+}
+
+func getAllPeople(happinessMap map[string]map[string]int) []string {
+	people := make([]string, 0, len(happinessMap))
+	for person := range happinessMap {
+		people = append(people, person)
+	}
+	return people
+}
+
+func generatePermutations(items []string) [][]string {
+	if len(items) == 0 {
+		return [][]string{{}}
+	}
+
+	var result [][]string
+	for idx, item := range items {
+		remaining := make([]string, len(items)-1)
+		copy(remaining[:idx], items[:idx])
+		copy(remaining[idx:], items[idx+1:])
+
+		for _, permutation := range generatePermutations(remaining) {
+			result = append(result, append([]string{item}, permutation...))
+		}
+	}
+	return result
+}
+
+func calculateTotalHappiness(arrangement []string, happinessMap map[string]map[string]int) int {
+	totalHappiness := 0
+	arrangementLength := len(arrangement)
+
+	for idx := range arrangementLength {
+		currentPerson := arrangement[idx]
+		leftNeighbor := arrangement[(idx-1+arrangementLength)%arrangementLength]
+		rightNeighbor := arrangement[(idx+1)%arrangementLength]
+
+		totalHappiness += happinessMap[currentPerson][leftNeighbor]
+		totalHappiness += happinessMap[currentPerson][rightNeighbor]
+	}
+
+	return totalHappiness
+}
+
+func ParseInput(filepath string) []string {
+	content, _ := os.ReadFile(filepath)
+	return strings.Split(string(content), "\n")
+}
+
+func PartOne(data []string) int {
+	happinessMap := buildHappinessMap(data)
+	allPeople := getAllPeople(happinessMap)
+
+	fixedPerson := allPeople[0]
+	remainingPeople := allPeople[1:]
+	permutations := generatePermutations(remainingPeople)
+
+	maxHappiness := math.MinInt
+	arrangement := make([]string, len(allPeople))
+	arrangement[0] = fixedPerson
+
+	for _, perm := range permutations {
+		copy(arrangement[1:], perm)
+		totalHappiness := calculateTotalHappiness(arrangement, happinessMap)
+		if totalHappiness > maxHappiness {
+			maxHappiness = totalHappiness
+		}
+	}
+
+	return maxHappiness
+}
+
+func PartTwo(data []string) int {
+	return 0
+}