feat: solve part one with brute-force and permutation enumeration

internal/2015/DayNine/code.go

@@ -0,0 +1,79 @@
+package daynine
+
+import (
+	"os"
+	"strconv"
+	"strings"
+
+	"advent-of-code/internal/registry"
+)
+
+func init() {
+	registry.Register("2015D9", ParseInput, PartOne, PartTwo)
+}
+
+func ParseInput(filepath string) []string {
+	content, _ := os.ReadFile(filepath)
+	return strings.Split(string(content), "\n")
+}
+
+func PartOne(data []string) int {
+	distances := make(map[string]map[string]int)
+
+	for _, line := range data {
+		parts := strings.Split(line, " = ")
+		distance, _ := strconv.Atoi(parts[1])
+		route := strings.Split(parts[0], " to ")
+		from, to := route[0], route[1]
+
+		if distances[from] == nil {
+			distances[from] = make(map[string]int)
+		}
+		if distances[to] == nil {
+			distances[to] = make(map[string]int)
+		}
+
+		distances[from][to] = distance
+		distances[to][from] = distance
+	}
+
+	cities := make([]string, 0, len(distances))
+	for city := range distances {
+		cities = append(cities, city)
+	}
+
+	var generatePermutations func([]string) [][]string
+	generatePermutations = func(cities []string) [][]string {
+		if len(cities) == 0 {
+			return [][]string{{}}
+		}
+		var result [][]string
+		for idx, city := range cities {
+			remaining := make([]string, len(cities)-1)
+			copy(remaining[:idx], cities[:idx])
+			copy(remaining[idx:], cities[idx+1:])
+
+			for _, permutations := range generatePermutations(remaining) {
+				result = append(result, append([]string{city}, permutations...))
+			}
+		}
+		return result
+	}
+
+	minimalDistance := int(^uint(0) >> 1)
+	for _, route := range generatePermutations(cities) {
+		total := 0
+		for idx := 0; idx < len(route)-1; idx++ {
+			total += distances[route[idx]][route[idx+1]]
+		}
+		if total < minimalDistance {
+			minimalDistance = total
+		}
+	}
+
+	return minimalDistance
+}
+
+func PartTwo(data []string) int {
+	return 0
+}