Clean up day 4 a bit

day4/go/main.go

@@ -27,6 +27,18 @@ func isValidPart1Password(password int) bool {
 	return hasDoubleDigitPair
 }
 
+// getAllPart1Passwords gets all valid passwords for part 1 in [lowerBound, upperBound]
+func getAllPart1Passwords(lowerBound, upperBound int) []int {
+	res := []int{}
+	for password := lowerBound; password <= upperBound; password++ {
+		if isValidPart1Password(password) {
+			res = append(res, password)
+		}
+	}
+
+	return res
+}
+
 func isValidPart2Password(password int) bool {
 	// The part 2 rules are stricter than part 1; they must be a valid part 1 password
 	if !isValidPart1Password(password) {
@@ -36,6 +48,7 @@ func isValidPart2Password(password int) bool {
 	lastChar := rune(0)
 	charCount := 0
 	passwordStr := strconv.Itoa(password)
+	// We will define an isolated pair to be a set like 22, but not 222
 	hasIsolatedRepeatedPair := false
 	for _, char := range passwordStr {
 		if lastChar == char {
@@ -74,15 +87,10 @@ func main() {
 		panic(fmt.Sprintf("could not parse upper bound: %s", err))
 	}
 
-	part1Passwords := []int{}
-	for password := lowerBound; password <= upperBound; password++ {
-		if isValidPart1Password(password) {
-			part1Passwords = append(part1Passwords, password)
-		}
-	}
-
+	part1Passwords := getAllPart1Passwords(lowerBound, upperBound)
 	fmt.Println(len(part1Passwords))
 
+	// We can save some computation by just going over our existing part 1 passwords for part 2
 	numPart2Passwords := 0
 	for _, password := range part1Passwords {
 		if isValidPart2Password(password) {