Initial commit - should have done this on day 1...

Q02.cs

@@ -0,0 +1,101 @@
+using System;
+using System.Collections.Generic;
+using System.Diagnostics;
+using System.IO;
+using System.Text.RegularExpressions;
+
+namespace _2020
+{
+   class Q02
+   {
+      public static void Go()
+      {
+         var list = GetList();
+         Part1(list);
+         Part2(list);
+      }
+
+      struct Q2Entry
+      {
+         public int first;
+         public int second;
+         public char ch;
+         public string pw;
+      }
+
+      static List<Q2Entry> GetList()
+      {
+         var list = new List<Q2Entry>();
+
+         using var fs = new FileStream("02input.txt", FileMode.Open);
+         using var sr = new StreamReader(fs);
+         string line;
+         var rule02 = new Regex("(?<min>[0-9]+)-(?<max>[0-9]+) (?<ch>[a-z]): (?<pw>.+)", RegexOptions.Compiled);
+         while ((line = sr.ReadLine()) != null)
+         {
+            var match = rule02.Match(line);
+            if (match.Success)
+            {
+               list.Add(new Q2Entry()
+               {
+                  first = Convert.ToInt32(match.Groups["min"].Value),
+                  second = Convert.ToInt32(match.Groups["max"].Value),
+                  ch = match.Groups["ch"].Value[0],
+                  pw = match.Groups["pw"].Value,
+               });
+            }
+         }
+
+         return list;
+      }
+
+      static void Part1(List<Q2Entry> list)
+      {
+         int numValid = 0;
+
+         foreach (var entry in list)
+         {
+            var numFound = 0;
+            foreach (var ch in entry.pw)
+            {
+               if (ch == entry.ch)
+               {
+                  numFound++;
+               }
+            }
+
+            if (numFound >= entry.first && numFound <= entry.second)
+            {
+               numValid++;
+            }
+         }
+
+         Debug.WriteLine($"Q02Part1: numValid={numValid}");
+      }
+
+      static void Part2(List<Q2Entry> list)
+      {
+         int numValid = 0;
+
+         foreach (var entry in list)
+         {
+            var validConditions = 0;
+            if (entry.pw.Length >= entry.first && entry.pw[entry.first - 1] == entry.ch)
+            {
+               validConditions++;
+            }
+            if (entry.pw.Length >= entry.second && entry.pw[entry.second - 1] == entry.ch)
+            {
+               validConditions++;
+            }
+
+            if (validConditions == 1)
+            {
+               numValid++;
+            }
+         }
+
+         Debug.WriteLine($"Q02Part2: numValid={numValid}");
+      }
+   }
+}