solution for day 4 (thanks i hate it)

2020/Day04.cs

@@ -0,0 +1,193 @@
+using System;
+using static System.Console;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+using System.Text.RegularExpressions;
+using Xunit;
+
+namespace AdventOfCode {
+
+  public class Day04 {
+
+    static string[] requiredFields = {
+      // "cid" not required because we are hackers
+      "byr", "iyr", "eyr", "hgt", "hcl", "ecl", "pid"
+    };
+
+    static string[] validEyeColors = {
+      "amb", "blu", "brn", "gry", "grn", "hzl", "oth"
+    };
+
+    static bool IsValidPassport1(string input) {
+      string[] fields = input.Split(' ');
+      var fieldsPresent = new HashSet<string>();
+      foreach (string field in fields) {
+        string[] tokens = field.Split(':');
+        string key = tokens[0];
+        fieldsPresent.Add(key);
+      }
+      return fieldsPresent.IsSupersetOf(requiredFields);
+    }
+
+    static int ParseInt(string value) {
+      int result;
+      if (!int.TryParse(value, out result)) {
+        return -1;
+      }
+      return result;
+    }
+
+    static bool IsValidPassport2(string input) {
+      string[] fields = input.Split(' ');
+      var fieldsPresent = new HashSet<string>();
+      foreach (string field in fields) {
+        if (field.Length == 0) {
+          continue;
+        }
+        string[] tokens = field.Split(':');
+        string key = tokens[0];
+        string value = tokens[1];
+        fieldsPresent.Add(key);
+        if (key == "byr") {
+          int year = ParseInt(value);
+          if (year < 1920 || year > 2002) {
+            return false;
+          }
+        } else if (key == "iyr") {
+          int year = ParseInt(value);
+          if (year < 2010 || year > 2020) {
+            return false;
+          }
+        } else if (key == "eyr") {
+          int year = ParseInt(value);
+          if (year < 2020 || year > 2030) {
+            return false;
+          }
+        } else if (key == "hgt") {
+          string unit = value.Substring(value.Length - 2);
+          int amount = ParseInt(value.Substring(0, value.Length - 2));
+          if (unit == "cm") {
+            if (amount < 150 || amount > 193) {
+              return false;
+            }
+          } else if (unit == "in") {
+            if (amount < 59 || amount > 76) {
+              return false;
+            }
+          } else {  // not cm or in
+            return false;
+          }
+        } else if (key == "hcl") {
+          Regex color = new Regex(@"^#[0-9a-f]{6}$");
+          if (!color.IsMatch(value)) {
+            return false;
+          }
+        } else if (key == "ecl") {
+          if (!validEyeColors.Contains(value)) {
+            return false;
+          }
+        } else if (key == "pid") {
+          Regex pid = new Regex(@"^[0-9]{9}$");
+          if (!pid.IsMatch(value)) {
+            return false;
+          }
+        }
+      }
+      return fieldsPresent.IsSupersetOf(requiredFields);
+    }
+
+    static List<string> ParsePassports(string[] input) {
+      var result = new List<string>();
+      string passport = "";
+      foreach (string line in input) {
+        if (line == "") {
+          result.Add(passport);
+          passport = "";
+        } else {
+          passport += line + " ";
+        }
+      }
+      result.Add(passport);
+      return result;
+    }
+
+    static int CountValidPassports1(string[] input) {
+      return ParsePassports(input).Count(IsValidPassport1);
+    }
+
+    static int CountValidPassports2(string[] input) {
+      return ParsePassports(input).Count(IsValidPassport2);
+    }
+
+    static int Part1() {
+      string[] input = File.ReadAllLines(Util.RootDir + "day04.txt");
+      return CountValidPassports1(input);
+    }
+
+    static int Part2() {
+      string[] input = File.ReadAllLines(Util.RootDir + "day04.txt");
+      return CountValidPassports2(input);
+    }
+
+    [Fact]
+    public static void Test() {
+      string[] example =
+@"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".Split('\n');
+
+      Assert.Equal(2, CountValidPassports1(example));
+      Assert.Equal(256, Part1());
+
+      string[] invalidPassports =
+@"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".Split('\n');
+
+      string[] validPassports =
+@"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".Split('\n');
+
+      List<string> invalid = ParsePassports(invalidPassports);
+      Assert.Equal(4, invalid.Count);
+      Assert.All(invalid, item => Assert.False(IsValidPassport2(item)));
+
+      List<string> valid = ParsePassports(validPassports);
+      Assert.Equal(4, valid.Count);
+      Assert.All(valid, item => Assert.True(IsValidPassport2(item)));
+
+      Assert.Equal(198, Part2());
+    }
+  }
+}

2020/Program.cs

@@ -19,7 +19,7 @@ namespace AdventOfCode {
 
   public class Program {
     static void Main(string[] args) {
-      Day03.Test();
+      Day04.Test();
     }
   }
 }