AdventOfCodeDay5.cs

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

namespace AdventOfCodeDay5
{
	class MainClass
	{
		public static void Main (string[] args)
		{
			StreamReader ss = new StreamReader ("../../input.txt");

			string line;
			var input = new List<string> ();
			while((line = ss.ReadLine()) != null)
			{
				input.Add (line);
			}

			var nice1 = input
				.Where (a => a.Sum (c => (c == 'a' || c == 'e' || c == 'i' || c == 'o' || c == 'u') ? 1 : 0) >= 3)
				.Where (b => b.Select ((c, i) => b.Substring (i).TakeWhile (x => x == c).Count ()).Max () > 1)
				.Where (d => !(d.Contains ("ab") || d.Contains ("cd") || d.Contains ("pq") || d.Contains ("xy")))
				.ToList ();

			var nice2 = input
				.Where (a => ContainsDoublePair(a))
				.Where (a=> ContainsSeparatedDouble(a))
				.ToList ();

			foreach(var s in nice2)
			{
				Console.WriteLine(s);
			}

			Console.WriteLine ($"Part 1 Nice Strings: {nice1.Count()}");
			Console.WriteLine ($"Part 2 Nice Strings: {nice2.Count()}");
		}

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

			for (int i = 0; i < s.Length - 1; i++) {
				var pair = s.Substring (i, 2);
				pairs.Add (new Tuple<string, int>(pair, i));
			}

			var doublePairs = pairs.Where (a => pairs.Sum(b=>b.Item1 == a.Item1 ? 1 : 0) > 1);

			if (doublePairs.Count () > 0) {

				var min = doublePairs.Min (a => a.Item2);
				var max = doublePairs.Max (a => a.Item2);
				return (max - min) > 1;
			}

			return false;
		}

		public static bool ContainsSeparatedDouble(string s)
		{
			for (int i = 0; i < s.Length - 2; i++) {
				if (s [i] == s [i + 2])
					return true;
			}

			return false;
		}
	}
}