Day 3 solution. Not clean, but oh well.

advent-of-code-2021.csproj

@@ -24,6 +24,9 @@
 	  <None Update="inputs\02.txt">
 	    <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
 	  </None>
+	  <None Update="inputs\03.txt">
+	    <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
+	  </None>
 	</ItemGroup>
 
 </Project>

src/03.cs

@@ -0,0 +1,129 @@
+namespace aoc2021
+{
+    internal class Day03
+    {
+        internal static void Go()
+        {
+            var lines = File.ReadAllLines("inputs/03.txt");
+            Part1(lines);
+            Part2(lines);
+        }
+
+        private static void Part1(IEnumerable<string> lines)
+        {
+            using var t = new Timer();
+            var len = lines.First().Length;
+            int gammaRate = 0;
+            int epsilonRate = 0;
+            for (int i = 0; i < len; i++)
+            {
+                var numZero = 0;
+                var numOne = 0;
+                foreach (var line in lines)
+                {
+                    if (line[i] == '0')
+                    {
+                        numZero++;
+                    }
+                    else if (line[i] == '1')
+                    {
+                        numOne++;
+                    }
+                }
+
+                if (numOne > numZero)
+                {
+                    gammaRate |= (1 << (len - i - 1));
+                }
+                else if (numZero > numOne)
+                {
+                    epsilonRate |= (1 << (len - i - 1));
+                }
+            }
+
+            Logger.Log($"part1: gamma rate: {gammaRate}, epsilon rate: {epsilonRate}, mult: {gammaRate * epsilonRate}");
+        }
+
+        private static void Part2(IEnumerable<string> lines)
+        {
+            using var t = new Timer();
+            int o2 = 0;
+            int co2 = 0;
+            var filtered = lines.ToList();
+            for (int i = 0; i < lines.First().Length; i++)
+            {
+                var numZero = 0;
+                var numOne = 0;
+                foreach (var line in filtered)
+                {
+                    if (line[i] == '0')
+                    {
+                        numZero++;
+                    }
+                    else if (line[i] == '1')
+                    {
+                        numOne++;
+                    }
+                }
+
+                if (numOne > numZero)
+                {
+                    filtered.RemoveAll(x => x[i] != '1');
+                }
+                else if (numZero > numOne)
+                {
+                    filtered.RemoveAll(x => x[i] != '0');
+                }
+                else
+                {
+                    filtered.RemoveAll(x => x[i] != '1');
+                }
+
+                if (filtered.Count == 1)
+                {
+                    o2 = Convert.ToInt32(filtered[0], 2);
+                    break;
+                }
+            }
+
+            filtered = lines.ToList();
+            for (int i = 0; i < lines.First().Length; i++)
+            {
+                var numZero = 0;
+                var numOne = 0;
+                foreach (var line in filtered)
+                {
+                    if (line[i] == '0')
+                    {
+                        numZero++;
+                    }
+                    else if (line[i] == '1')
+                    {
+                        numOne++;
+                    }
+                }
+
+                if (numOne < numZero)
+                {
+                    filtered.RemoveAll(x => x[i] != '1');
+                }
+                else if (numZero < numOne)
+                {
+                    filtered.RemoveAll(x => x[i] != '0');
+                }
+                else
+                {
+                    filtered.RemoveAll(x => x[i] != '0');
+                }
+
+                if (filtered.Count == 1)
+                {
+                    co2 = Convert.ToInt32(filtered[0], 2);
+                    break;
+                }
+            }
+
+            Logger.Log($"o2*co2 = {o2} * {co2} = {o2 * co2}");
+        }
+    }
+}

src/main.cs

@@ -1 +1,2 @@
 aoc2021.Day02.Go();
+aoc2021.Day03.Go();