AdventOfCodeDay6.cs

using System;
using System.IO;
using System.Collections.Generic;
using System.Linq;
using System.Text.RegularExpressions;
using System.Drawing;
using System.Drawing.Imaging;

namespace AdventOfCodeDay6
{
	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 re = new Regex (@".*?(?<X1>[0-9]+),(?<Y1>[0-9]+) through (?<X2>[0-9]+),(?<Y2>[0-9]+)", RegexOptions.Compiled | RegexOptions.CultureInvariant | RegexOptions.IgnoreCase);

			var lights1 = new int[1000, 1000];
			var lights2 = new int[1000, 1000];

			foreach (var c in input) {
			
				Command command = Command.Toggle;
				if (c.StartsWith ("toggle"))
					command = Command.Toggle;
				if (c.StartsWith ("turn off"))
					command = Command.TurnOff;
				if (c.StartsWith ("turn on"))
					command = Command.TurnOn;

				var m = re.Matches (c) [0];
				 
				var x1 = int.Parse (m.Groups ["X1"].Value);
				var y1 = int.Parse (m.Groups ["Y1"].Value);
				var x2 = int.Parse (m.Groups ["X2"].Value);
				var y2 = int.Parse (m.Groups ["Y2"].Value);

				//Console.WriteLine ($"{command} ({x1}, {y1}) to ({x2}, {y2})");

				ProcessCommand1 (lights1, command, x1, y1, x2, y2);
				ProcessCommand2 (lights2, command, x1, y1, x2, y2);
			}

			int onCount = 0;
			int brightness = 0;
			for (int x = 0; x < 1000; x++) {
				for (int y = 0; y < 1000; y++) {
					onCount += lights1 [x, y];
					brightness += lights2 [x, y];
				}
			}

			SaveImage (lights1, "part1.png");
			SaveImage (lights2, "part2.png");

			Console.WriteLine ($"Lights On: {onCount}");
			Console.WriteLine ($"Lights On: {brightness}");
		}

		public static void ProcessCommand1 (int[,] lights, Command cmd, int x1, int y1, int x2, int y2)
		{
			for (int x = x1; x <= x2; x++) {
				for (int y = y1; y <= y2; y++) {
					if (cmd == Command.Toggle) {
						lights [x, y] = 1-lights [x, y];
					} else if (cmd == Command.TurnOff) {
						lights [x, y] = 0;
					} else if (cmd == Command.TurnOn) {
						lights [x, y] = 1;
					}
				}
			}
		}

		public static void ProcessCommand2 (int[,] lights, Command cmd, int x1, int y1, int x2, int y2)
		{
			for (int x = x1; x <= x2; x++) {
				for (int y = y1; y <= y2; y++) {
					if (cmd == Command.Toggle) {
						lights [x, y] += 2;
					} else if (cmd == Command.TurnOff) {
						if (lights [x, y] > 0)
							lights [x, y]--;
					} else if (cmd == Command.TurnOn) {
						lights [x, y]++;
					}
				}
			}
		}

		public static void SaveImage (int[,] lights, string fileName)
		{
			using (Bitmap b = new Bitmap (1000, 1000)) {

				var max = 0;
				for (int x = 0; x < 1000; x++) {
					for (int y = 0; y < 1000; y++) {
						max = Math.Max (max, lights [x, y]);
					}
				}

				for (int x = 0; x < 1000; x++) {
					for (int y = 0; y < 1000; y++) {

						int v = lights [x, y];

						int cv = (int)(((double)v / max) * 255.0);
						b.SetPixel (x, y, Color.FromArgb (0xff, cv, cv, cv));
					}
				}
				b.Save ($"../../{fileName}", ImageFormat.Png);
			}
		}

		public enum Command
		{
			Toggle,
			TurnOn,
			TurnOff
		}
	}
}