AdventOfCodeDay11.cs

using System;
using System.Collections.Generic;
using System.Linq;

namespace AdventOfCodeDay11
{
	class Program
	{
		static void Main(string[] args)
		{
			var password = "hxbxwxba".Reverse().ToArray();

			var cnt = 0;

			var start = DateTime.Now;

			var foundCount = 0;

			do
			{
				for (var i = 0; i < password.Length; i++)
				{
					bool carry;

					if (password[i] == 'z')
					{
						password[i] = 'a';
						carry = true;
					}
					else
					{
						password[i]++;
						carry = false;
					}

					if (password[i] == 'i' || password[i] == 'o' || password[i] == 'l') password[i]++;

					if (!carry) break;
				}
				cnt++;

				if (cnt % 1000000 == 0)
				{
					var p = new string(password.Reverse().ToArray());
					var sec = (DateTime.Now - start).TotalSeconds;
					var ps = Math.Round(cnt / sec);
					Console.WriteLine($"{cnt} : {p} : {ps}/sec");
				}

				if (TestPassword(password.Reverse().ToArray()))
				{
					foundCount++;
					Console.WriteLine($"{foundCount} : {cnt}: {new string(password.Reverse().ToArray())}");
				}

			} while (foundCount <= 5);

			Console.WriteLine($"{cnt}: {new string(password.Reverse().ToArray())}");

			Console.WriteLine("Done");
			Console.ReadLine();
		}

		private static bool TestPassword(char[] password)
		{
			return ContainsThreeLetterRun(password) && ContainsDoublePair(password);
		}

		public static bool ContainsThreeLetterRun(char[] s)
		{
			for (var i = 0; i < s.Length - 2; i++)
			{
				if ((s[i] + 1) == s[i + 1] && (s[i] + 2) == s[i + 2])
				{
					return true;
				}
			}
			return false;
		}

		public static bool ContainsDoublePair(char[] s)
		{
			var pairs = new List<Tuple<string, int>>();

			for (var i = 0; i < s.Length - 1; i++)
			{
				var pair = $"{s[i]}{s[i + 1]}";
				if (pair[0] == pair[1] && pairs.All(a => a.Item1 != pair))
				{
					pairs.Add(new Tuple<string, int>(pair, i));
				}
			}

			return pairs.Count > 1;
		}
	}
}