Adv2015/D19.2/Program.cs

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

namespace D19._2
{
    class Program
    {
        static void Main(string[] args)
        {
            if (args.Length < 1) throw new ArgumentException();
            if (File.Exists(args[0]) == false) throw new FileNotFoundException();

            string input;
            List<(string, string)> replacements;
            _1.Program.ParseFile(args, out input, out replacements);

            replacements = replacements.Select(r => (r.Item2, r.Item1)).ToList();

            var steps = TestMolecules(input, "e", replacements);

            Console.WriteLine($"The answer is : {steps}");
        }

        private static void ParseFile(string[] args, out string input, out List<(string, string)> replacements)
        {
            input = string.Empty;
            replacements = new List<(string, string)>();
            using (var file = File.OpenText(args[0]))
            {
                while (true)
                {
                    var line = file.ReadLine();
                    if (line == null) break;

                    if (line == string.Empty) continue;

                    var lr = line.Split(" => ");

                    if (lr.Length == 2) replacements.Add((lr[0], lr[1]));
                    else input = lr[0];
                }
            }
        }

        private static int TestMolecules(string input, string find, List<(string, string)> replacements)
        {
            var tested = new HashSet<string>();
            var buildQueue = new List<(string molecule, int step)>();

            buildQueue.Add((input, 0));

            while (buildQueue.Count > 0)
            {
                (var mol, int step) = buildQueue.ElementAt(0);
                buildQueue.RemoveAt(0);

                input = mol;
                tested.Add(input);

                if (input == find) return step;

                foreach (var molecule in _1.Program.TestMolecules(input, replacements).OrderByDescending(s => s.Length))
                {
                    if (tested.Contains(molecule) == false)
                        buildQueue.Insert(0, (molecule, step + 1));
                }
            }

            return 0;
        }
    }
}