Adv2016/D18.1/Program.cs

using System;
using System.IO;
using System.Linq;

namespace D18._1
{
    class Program
    {
        static void Main(string[] args)
        {
            string input = File.ReadAllText(args[0]).Trim();

            Console.WriteLine($"Part 1 : There is {CountSafeTiles(input, 40)} safe tiles.");
            Console.WriteLine($"Part 2 : There is {CountSafeTiles(input, 400000)} safe tiles.");
        }

        private static int CountSafeTiles(string input, int rows)
        {
            var line = new bool[input.Length];
            int safe = 0;
            for (var i = 0; i < input.Length; ++i)
            {
                line[i] = input[i] == '^' ? true : false;
                if (line[i] == false) safe++;
            }

            for (var r = 1; r < rows; ++r)
            {
                var nline = new bool[line.Length];
                for (var i = 0; i < line.Length; ++i)
                {
                    var left = i == 0 ? false : line[i - 1];
                    var center = line[i];
                    var right = i == line.Length - 1 ? false : line[i + 1];

                    if (left && center && right == false) nline[i] = true;
                    else if (center && right && left == false) nline[i] = true;
                    else if (left && center == false && right == false) nline[i] = true;
                    else if (left == false && center == false && right) nline[i] = true;
                    else safe++;
                }
                line = nline;
            }

            return safe;
        }
    }
}