Day04.cs

using System.Text.RegularExpressions;

namespace AdventOfCode._2020;

public class Day04
{
    private string _input;

    public Day04()
    {
        _input = File.ReadAllText("Inputs/Day04.txt");
    }

    [Fact]
    public void Part1()
    {
        MatchCollection matches = s_Regex.Matches(_input);
        int answer = matches.Count(m =>
        {
            Group group = m.Groups["key"];
            if (group.Captures.Count == 7 && m.Value.Contains("cid"))
                return false;

            return true;
        });

        Assert.Equal(230, answer);
    }

    [Fact]
    public void Part2()
    {
        MatchCollection matches = s_Regex2.Matches(_input);

        int answer = matches.Count(m =>
        {
            CaptureCollection captures = m.Groups["x"].Captures;

            foreach (Capture capture in captures)
            {
                string[] tokens = capture.Value.Split(':');
                string key = tokens[0];
                string value = tokens[1];

                if (key == "cid" && captures.Count == 7)
                    return false;

                int num = 0;
                if (int.TryParse(value, out num))
                {
                    if ((key == "byr" && num is < 1920 or > 2002) ||
                        (key == "iyr" && num is < 2010 or > 2020) ||
                        (key == "eyr" && num is < 2020 or > 2030))
                        return false;
                }
                else if (key == "hgt")
                {
                    num = int.Parse(value.Substring(0, value.Length - 2));
                    if (value.EndsWith("cm"))
                    {
                        if (num is < 150 or > 193)
                            return false;
                    }
                    else if (num is < 59 or > 76)
                        return false;
                }
            }

            return true;
        });

        Assert.Equal(156, answer);
    }

    private static Regex s_Regex = new Regex(
        @"(?'value'(?'key'byr|iyr|eyr|hgt|hcl|ecl|pid|cid):[#\w]+( |\r?\n)?){7,8}",
        RegexOptions.Compiled);

    private static Regex s_Regex2 = new Regex(
        @"((?'x'(byr|iyr|eyr):\d{4}|hgt:\d{2,3}(cm|in)|hcl:#[a-f0-9]{6}|ecl:(amb|blu|brn|gry|grn|hzl|oth)|pid:\d{9}|cid:\w+)( |\r?\n)?){7,8}",
        RegexOptions.Compiled);
}