refactor: extract reactPolymer to reuse it in PartTwo

internal/2018/DayFive/code.go

@@ -15,7 +15,7 @@ func ParseInput(filepath string) string {
 	return string(content)
 }
 
-func PartOne(data string) int {
+func reactPolymer(data string) int {
 	stack := []rune{}
 
 	for _, char := range data {
@@ -36,6 +36,10 @@ func PartOne(data string) int {
 	return len(stack)
 }
 
+func PartOne(data string) int {
+	return reactPolymer(data)
+}
+
 func PartTwo(data string) int {
 	return 0
 }