Adding Day 4 Solution

csharp/Day4Solution.cs

@@ -0,0 +1,47 @@
+using System;
+using System.IO;
+using System.Security.Cryptography;
+using System.Text;
+
+namespace AOC2015
+{
+    class Day4Solution : Solution
+    {
+        public override int Day => 4;
+        public override string Name => "Day 4: The Ideal Stocking Stuffer";
+
+        public override void Run()
+        {
+            string input = "yzbqklnj"; // Puzzle Input
+
+            Console.WriteLine($"Part 1 Answer: {Part1(input)}");
+            Console.WriteLine($"Part 2 Answer: {Part2(input)}");
+        }
+
+        private int Part1(string input)
+        {
+            MD5CryptoServiceProvider md5CryptoServiceProvider = new MD5CryptoServiceProvider();
+            for (int i = 0; i < int.MaxValue; i++)
+            {
+                byte[] hashBytes = md5CryptoServiceProvider.ComputeHash(Encoding.ASCII.GetBytes(input + i));
+                string hash = BitConverter.ToString(hashBytes).Replace("-", "").ToLower();
+                if (hash.StartsWith("00000"))
+                    return i;
+            }
+            return -1;
+        }
+
+        private int Part2(string input)
+        {
+            MD5CryptoServiceProvider md5CryptoServiceProvider = new MD5CryptoServiceProvider();
+            for (int i = 0; i < int.MaxValue; i++)
+            {
+                byte[] hashBytes = md5CryptoServiceProvider.ComputeHash(Encoding.ASCII.GetBytes(input + i));
+                string hash = BitConverter.ToString(hashBytes).Replace("-", "").ToLower();
+                if (hash.StartsWith("000000"))
+                    return i;
+            }
+            return -1;
+        }
+    }
+}