Discussion on: Advent of Code: 2020 Day 04

[Neil Gall]

I re-used and extended the parser combinators I wrote for day 2 (see, that investment is paying off already!) but I'm not entirely happy with my solution. My instinct was Parse don't validate but with AoC you never know what's coming in part 2. The bit about cheating the system in the initial description made me think the second part might have to deal with the invalid records in some way. So I kept the PasswordData as a simple HashMap for maximum flexibility. Now I know the full requirements I might come back later and implement a proper parse-don't-validate approach.

use std::collections::HashMap;
use std::fs::File;
use std::io::prelude::*;
use std::ops::RangeInclusive;
use std::str::Chars;

mod parser;
use parser::*;

// --- model

struct PassportData(HashMap<String, String>);

enum Height {
    CM(usize),
    IN(usize)
}

fn parse_height(input: &str) -> ParseResult<Height> {
    let p = or(
        map(seq(integer, string("cm")), |(h, _)| Height::CM(h as usize)),
        map(seq(integer, string("in")), |(h, _)| Height::IN(h as usize))
    );
    p.parse(input)
}

fn height_string_is_valid(s: &str) -> bool {
    if let Ok((_, height)) = parse_height(s) {
        match height {
            Height::CM(h) => (150..=193).contains(&h),
            Height::IN(h) => (59..=76).contains(&h)
        }
    } else {
        false
    }
}

fn has_n_digits(mut chars: Chars, n: usize, radix: u32) -> bool {
    (0..n).all(|_|
        chars.next().map(|c| c.is_digit(radix)).unwrap_or(false)
    ) && chars.next().is_none()
}

fn is_valid_hair_color(s: &str) -> bool {
    let mut chars = s.chars();
    chars.next() == Some('#') && has_n_digits(chars, 6, 16)
}

fn is_valid_eye_color(s: &str) -> bool {
    vec!["amb", "blu", "brn", "gry", "grn", "hzl", "oth"].contains(&s)
}

impl PassportData {
    fn new(data: Vec<(String,String)>) -> Self {
        PassportData(data.iter().cloned().collect())
    }

    fn contains_required_fields(&self) -> bool {
        vec!["byr", "iyr", "eyr", "hgt", "hcl", "ecl", "pid"]
            .into_iter()
            .all(|key| self.0.contains_key(key))
    }

    fn all_fields_are_valid(&self) -> bool {
        self.birth_year_is_valid()
        && self.issue_year_is_valid()
        && self.expiration_year_is_valid()
        && self.height_is_valid()
        && self.hair_color_is_valid()
        && self.eye_color_is_valid()
        && self.passport_id_is_valid()
    }

    fn year_is_valid(&self, key: &str, valid_range: RangeInclusive<usize>) -> bool {
        if let Some(s) = self.0.get(key) {
            if let Ok(byr) = s.parse::<usize>() {
                return valid_range.contains(&byr)
            }
        }
        false
    }

    fn birth_year_is_valid(&self) -> bool {
        self.year_is_valid("byr", 1920..=2002)
    }

    fn issue_year_is_valid(&self) -> bool {
        self.year_is_valid("iyr", 2010..=2020)
    }

    fn expiration_year_is_valid(&self) -> bool {
        self.year_is_valid("eyr", 2020..=2030)
    }

    fn height_is_valid(&self) -> bool {
        if let Some(s) = self.0.get("hgt") {
            height_string_is_valid(s)
        } else {
            false
        }
    }

    fn hair_color_is_valid(&self) -> bool {
        if let Some(s) = self.0.get("hcl") {
            is_valid_hair_color(s)
        } else {
            false
        }
    }

    fn eye_color_is_valid(&self) -> bool {
        if let Some(s) = self.0.get("ecl") {
            is_valid_eye_color(s)
        } else {
            false
        }
    }

    fn passport_id_is_valid(&self) -> bool {
        if let Some(s) = self.0.get("pid") {
            has_n_digits(s.chars(), 9, 10)
        } else {
            false
        }
    }
}

// --- input file

fn read_file(filename: &str) -> std::io::Result<String> {
    let mut file = File::open(filename)?;
    let mut contents = String::new();
    file.read_to_string(&mut contents)?;
    Ok(contents)
}

fn parse_input(input: &str) -> Vec<PassportData> {
    let tag = map(one_or_more(letter), |ls| ls.iter().collect());
    let value = map(one_or_more(non_whitespace), |cs| cs.iter().collect());
    let item = between(tag, string(":"), value);
    let passport = map(one_or_more(first(item, whitespace)), PassportData::new);

    input.split("\n\n")
        .map(|inp| passport.parse(inp).unwrap().1)
        .collect()
}


// --- problems

fn part1(data: &Vec<PassportData>) -> usize {
    data.iter().filter(|p| p.contains_required_fields()).count()
}

fn part2(data: &Vec<PassportData>) -> usize {
    data.iter().filter(|p| p.all_fields_are_valid()).count()
}

fn main() {
    let input = read_file("./input.txt").unwrap();
    let passport_data = parse_input(&input);
    println!("part1 {}", part1(&passport_data));
    println!("part2 {}", part2(&passport_data));
}

#[cfg(test)]
mod tests {
    use super::*;

    fn sample_input() -> &'static str {
"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"
    }

    #[test]
    fn test_parse_input() {
        let data = parse_input(sample_input());
        assert_eq!(data.len(), 4);

        vec![
            ("ecl", "gry"),
            ("pid", "860033327"),
            ("eyr", "2020"),
            ("hcl", "#fffffd"),
            ("byr", "1937"),
            ("iyr", "2017"),
            ("cid", "147"),
            ("hgt", "183cm")
        ].into_iter().for_each(|(k,v)| {
            assert_eq!(data[0].0.get(k), Some(&String::from(v)));
        });
    }

    #[test]
    fn test_has_required_fields() {
        let data = parse_input(sample_input());
        assert_eq!(data[0].contains_required_fields(), true);
        assert_eq!(data[1].contains_required_fields(), false);
        assert_eq!(data[2].contains_required_fields(), true);
        assert_eq!(data[3].contains_required_fields(), false);
    }

    #[test]
    fn test_invalid_passports() {
        let data = parse_input("eyr:1972 cid:100
hcl:#18171d ecl:amb hgt:170 pid:186cm iyr:2018 byr:1926

iyr:2019
hcl:#602927 eyr:1967 hgt:170cm
ecl:grn pid:012533040 byr:1946

hcl:dab227 iyr:2012
ecl:brn hgt:182cm pid:021572410 eyr:2020 byr:1992 cid:277

hgt:59cm ecl:zzz
eyr:2038 hcl:74454a iyr:2023
pid:3556412378 byr:2007");

        data.iter().for_each(|p| {
            assert_eq!(p.all_fields_are_valid(), false)
        });
    }

    #[test]
    fn test_valid_passports() {
        let data = parse_input("pid:087499704 hgt:74in ecl:grn iyr:2012 eyr:2030 byr:1980
hcl:#623a2f

eyr:2029 ecl:blu cid:129 byr:1989
iyr:2014 pid:896056539 hcl:#a97842 hgt:165cm

hcl:#888785
hgt:164cm byr:2001 iyr:2015 cid:88
pid:545766238 ecl:hzl
eyr:2022

iyr:2010 hgt:158cm hcl:#b6652a ecl:blu byr:1944 eyr:2021 pid:093154719");

        data.iter().for_each(|p| {
            assert_eq!(p.all_fields_are_valid(), true)
        });
    }

    #[test]
    fn test_height_validation() {
        assert_eq!(height_string_is_valid("60in"), true);
        assert_eq!(height_string_is_valid("190cm"), true);
        assert_eq!(height_string_is_valid("190in"), false);
        assert_eq!(height_string_is_valid("190"), false);
    }

    #[test]
    fn test_hair_color_validation() {
        assert_eq!(is_valid_hair_color("#123abc"), true);
        assert_eq!(is_valid_hair_color("#123abz"), false);
        assert_eq!(is_valid_hair_color("#123"), false);
        assert_eq!(is_valid_hair_color("123abc"), false);
        assert_eq!(is_valid_hair_color("#123abcd"), false);
    }

    #[test]
    fn test_eye_color_validation() {
        assert_eq!(is_valid_eye_color("brn"), true);
        assert_eq!(is_valid_eye_color("wat"), false);
    }
}

[Christopher Nilsson]

I'm guessing this is rust? I'm impressed by your structure! It's clear to understand the code and nice that you have tests! Hopefully I'll learn to add more tests as well some day 🙏 haha

[Neil Gall]

Thanks. Yes, it's Rust. I like to approach these problems as if I was producing production code. That's the only type worth practicing, right? :-)