refactor: create functions that we gonna use for part two

internal/2015/DayNine/code.go

@@ -17,7 +17,7 @@ func ParseInput(filepath string) []string {
 	return strings.Split(string(content), "\n")
 }
 
-func PartOne(data []string) int {
+func buildDistanceMap(data []string) map[string]map[string]int {
 	distances := make(map[string]map[string]int)
 
 	for _, line := range data {
@@ -37,13 +37,18 @@ func PartOne(data []string) int {
 		distances[to][from] = distance
 	}
 
+	return distances
+}
+
+func getCities(distances map[string]map[string]int) []string {
 	cities := make([]string, 0, len(distances))
 	for city := range distances {
 		cities = append(cities, city)
 	}
+	return cities
+}
 
-	var generatePermutations func([]string) [][]string
-	generatePermutations = func(cities []string) [][]string {
+func generatePermutations(cities []string) [][]string {
 	if len(cities) == 0 {
 		return [][]string{{}}
 	}
@@ -58,14 +63,24 @@ func PartOne(data []string) int {
 		}
 	}
 	return result
-	}
+}
 
-	minimalDistance := int(^uint(0) >> 1)
-	for _, route := range generatePermutations(cities) {
+func calculateRouteDistance(route []string, distances map[string]map[string]int) int {
 	total := 0
 	for idx := 0; idx < len(route)-1; idx++ {
 		total += distances[route[idx]][route[idx+1]]
 	}
+	return total
+}
+
+func PartOne(data []string) int {
+	distances := buildDistanceMap(data)
+	cities := getCities(distances)
+	permutations := generatePermutations(cities)
+
+	minimalDistance := int(^uint(0) >> 1)
+	for _, route := range permutations {
+		total := calculateRouteDistance(route, distances)
 		if total < minimalDistance {
 			minimalDistance = total
 		}