day 4, with an arbitrary constraint: I didn't want to use regexes.

04/main.go

@@ -0,0 +1,247 @@
+package main
+
+import (
+	"bufio"
+	"fmt"
+	"os"
+	"strconv"
+	"strings"
+)
+
+func main() {
+	partOne()
+	partTwo()
+}
+
+type passport struct {
+	byr string //(Birth Year)
+	iyr string //(Issue Year)
+	eyr string //(Expiration Year)
+	hgt string //(Height)
+	hcl string //(Hair Color)
+	ecl string //(Eye Color)
+	pid string //(Passport ID)
+	cid string //(Country ID)
+}
+
+func addToPassport(p *passport, i []string) {
+	if i[0] == "byr" {
+		p.byr = i[1]
+	}
+	if i[0] == "iyr" {
+		p.iyr = i[1]
+	}
+	if i[0] == "eyr" {
+		p.eyr = i[1]
+	}
+	if i[0] == "hgt" {
+		p.hgt = i[1]
+	}
+	if i[0] == "hcl" {
+		p.hcl = i[1]
+	}
+	if i[0] == "ecl" {
+		p.ecl = i[1]
+	}
+	if i[0] == "pid" {
+		p.pid = i[1]
+	}
+	if i[0] == "cid" {
+		p.cid = i[1]
+	}
+}
+
+func (p passport) IsPassport() bool {
+	return p.byr != "" && p.iyr != "" && p.eyr != "" && p.hgt != "" && p.hcl != "" && p.ecl != "" && p.pid != "" && p.cid != ""
+}
+
+func (p passport) IsCredentials() bool {
+	return p.byr != "" && p.iyr != "" && p.eyr != "" && p.hgt != "" && p.hcl != "" && p.ecl != "" && p.pid != "" && p.cid == ""
+}
+
+func (p passport) IsValid() bool {
+	// byr (Birth Year) - four digits; at least 1920 and at most 2002.
+	i, err := strconv.Atoi(p.byr)
+	if err != nil || i < 1920 || i > 2002 {
+		return false
+	}
+	// iyr (Issue Year) - four digits; at least 2010 and at most 2020.
+	i, err = strconv.Atoi(p.iyr)
+	if err != nil || i < 2010 || i > 2020 {
+		return false
+	}
+	// eyr (Expiration Year) - four digits; at least 2020 and at most 2030.
+	i, err = strconv.Atoi(p.eyr)
+	if err != nil || i < 2020 || i > 2030 {
+		return false
+	}
+	// hgt (Height) - a number followed by either cm or in:
+	// If cm, the number must be at least 150 and at most 193.
+	// If in, the number must be at least 59 and at most 76.
+	i, j, err := parseHeight(p.hgt)
+	if err != nil || (j != "in" && j != "cm") || (j == "in" && (i < 59 || i > 76)) || (j == "cm" && (i < 150 || i > 193)) {
+		return false
+	}
+	// hcl (Hair Color) - a # followed by exactly six characters 0-9 or a-f.
+	j, err = parseColor(p.hcl)
+	if err != nil || len(j) > 6 || len(j) < 1 {
+		return false
+	}
+	// ecl (Eye Color) - exactly one of: amb blu brn gry grn hzl oth.
+	if !(p.ecl == "amb" || p.ecl == "blu" || p.ecl == "brn" || p.ecl == "gry" || p.ecl == "grn" || p.ecl == "hzl" || p.ecl == "oth") {
+		return false
+	}
+	// pid (Passport ID) - a nine-digit number, including leading zeroes.
+	j, err = parsePassportID(p.pid)
+	if err != nil || len(j) != 9 {
+		return false
+	}
+	// cid (Country ID) - ignored, missing or not.
+	return true
+}
+
+func parseHeight(s string) (int, string, error) {
+	var measurement, unit []rune
+	for _, r := range s {
+		switch {
+		case r == 'c' || r == 'm' || r == 'i' || r == 'n':
+			unit = append(unit, r)
+		case r >= '0' && r <= '9':
+			measurement = append(measurement, r)
+		default:
+			return 0, "", fmt.Errorf("invalid")
+		}
+	}
+	m, err := strconv.Atoi(string(measurement))
+	return m, string(unit), err
+}
+
+func parseColor(s string) (string, error) {
+	var color []rune
+	for i, r := range s {
+		switch {
+		case (r == '#' && i != 0) || (r != '#' && i == 0):
+			return "", fmt.Errorf("invalid or missing #")
+		case r == '#' && i == 0:
+			continue
+		case (r >= '0' && r <= '9') || (r >= 'a' && r <= 'f'):
+			color = append(color, r)
+		default:
+			return "", fmt.Errorf("invalid rune")
+		}
+	}
+	return string(color), nil
+}
+
+func parsePassportID(s string) (string, error) {
+	var number []rune
+	for _, r := range s {
+		switch {
+		case (r >= '0' && r <= '9'):
+			number = append(number, r)
+		default:
+			return "", fmt.Errorf("invalid")
+		}
+	}
+	return string(number), nil
+}
+
+// Passport data is validated in batch files (your puzzle input).
+// Each passport is represented as a sequence of key:value pairs separated by spaces or newlines.
+// Passports are separated by blank lines.
+// Here is an example batch file containing four passports:
+//
+// ecl:gry pid:860033327 eyr:2020 hcl:#fffffd
+// byr:1937 iyr:2017 cid:147 hgt:183cm
+//
+// iyr:2013 ecl:amb cid:350 eyr:2023 pid:028048884
+// hcl:#cfa07d byr:1929
+//
+// hcl:#ae17e1 iyr:2013
+// eyr:2024
+// ecl:brn pid:760753108 byr:1931
+// hgt:179cm
+//
+// hcl:#cfa07d eyr:2025 pid:166559648
+// iyr:2011 ecl:brn hgt:59in
+//
+// The first passport is valid - all eight fields are present.
+// The second passport is invalid - it is missing hgt (the Height field).
+// The third passport is interesting; the only missing field is cid, so it looks like data from North Pole Credentials, not a passport at all!
+// Surely, nobody would mind if you made the system temporarily ignore missing cid fields. Treat this "passport" as valid.
+// The fourth passport is missing two fields, cid and byr.
+// Missing cid is fine, but missing any other field is not, so this passport is invalid.
+// According to the above rules, your improved system would report 2 valid passports.
+// Count the number of valid passports - those that have all required fields.
+// Treat cid as optional. In your batch file, how many passports are valid?
+
+func partOne() {
+	f, _ := os.Open("input")
+	reader := bufio.NewReader(f)
+	scanner := bufio.NewScanner(reader)
+
+	valid := 0
+	current := passport{}
+
+	for scanner.Scan() {
+		line := scanner.Text()
+		if line == "" {
+			if current.IsCredentials() || current.IsPassport() {
+				valid = valid + 1
+			}
+			current = passport{}
+		} else {
+			for _, entry := range strings.Split(line, " ") {
+				addToPassport(&current, strings.Split(entry, ":"))
+			}
+		}
+	}
+	// finally, check the final entry
+	if current.IsCredentials() || current.IsPassport() {
+		valid = valid + 1
+	}
+
+	fmt.Println(valid)
+}
+
+// You can continue to ignore the cid field, but each other field has strict rules about what values are valid for automatic validation:
+// byr (Birth Year) - four digits; at least 1920 and at most 2002.
+// iyr (Issue Year) - four digits; at least 2010 and at most 2020.
+// eyr (Expiration Year) - four digits; at least 2020 and at most 2030.
+// hgt (Height) - a number followed by either cm or in:
+// If cm, the number must be at least 150 and at most 193.
+// If in, the number must be at least 59 and at most 76.
+// hcl (Hair Color) - a # followed by exactly six characters 0-9 or a-f.
+// ecl (Eye Color) - exactly one of: amb blu brn gry grn hzl oth.
+// pid (Passport ID) - a nine-digit number, including leading zeroes.
+// cid (Country ID) - ignored, missing or not.
+// Your job is to count the passports where all required fields are both present and valid according to the above rules.
+
+func partTwo() {
+	f, _ := os.Open("input")
+	reader := bufio.NewReader(f)
+	scanner := bufio.NewScanner(reader)
+
+	valid := 0
+	current := passport{}
+
+	for scanner.Scan() {
+		line := scanner.Text()
+		if line == "" {
+			if current.IsValid() {
+				valid = valid + 1
+			}
+			current = passport{}
+		} else {
+			for _, entry := range strings.Split(line, " ") {
+				addToPassport(&current, strings.Split(entry, ":"))
+			}
+		}
+	}
+	// finally, check the final entry
+	if current.IsValid() {
+		valid = valid + 1
+	}
+
+	fmt.Println(valid)
+}