Year2018Day20.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Text.RegularExpressions;
using AdventOfCode.Common;
using JetBrains.Annotations;
using RoyT.AStar;

namespace AdventOfCode.Solutions._2018._20;

[UsedImplicitly]
public class Year2018Day20 : ISolution
{
	public object Part1(IEnumerable<string> input)
	{
		var paths = input.First()[1..^1];
		var (x, y) = (5000, 5000);

		var positions = new Stack<(int x, int y)>();
		var (prevX, prevY) = (x, y);
		var distances = new Dictionary<(int x, int y), int>();
		var directions = new Dictionary<char, (int x, int y)>
		{
			['N'] = (0, -1),
			['E'] = (1, 0),
			['S'] = (0, 1),
			['W'] = (-1, 0)
		};
		foreach (var c in paths)
		{
			switch (c)
			{
				case '(':
					positions.Push((x, y));
					break;
				case ')':
					(x, y) = positions.Pop();
					break;
				case '|':
					(x, y) = positions.First();
					break;
				default:
				{
					var (dx, dy) = directions[c];
					x += dx;
					y += dy;

					if (distances.ContainsKey((x, y)))
						distances[(x, y)] = Math.Min(distances[(x, y)], distances[(prevX, prevY)] + 1);
					else
						distances[(x, y)] = distances.GetValueOrDefault((prevX, prevY), 0) + 1;
					break;
				}
			}

			(prevX, prevY) = (x, y);
		}
			
		return distances.Values.Max().ToString();
	}
		
	public object Part2(IEnumerable<string> input)
	{
		var paths = input.First()[1..^1];
		var (x, y) = (5000, 5000);

		var positions = new Stack<(int x, int y)>();
		var (prevX, prevY) = (x, y);
		var distances = new Dictionary<(int x, int y), int>();
		var directions = new Dictionary<char, (int x, int y)>
		{
			['N'] = (0, -1),
			['E'] = (1, 0),
			['S'] = (0, 1),
			['W'] = (-1, 0)
		};
		foreach (var c in paths)
		{
			switch (c)
			{
				case '(':
					positions.Push((x, y));
					break;
				case ')':
					(x, y) = positions.Pop();
					break;
				case '|':
					(x, y) = positions.First();
					break;
				default:
				{
					var (dx, dy) = directions[c];
					x += dx;
					y += dy;

					if (distances.ContainsKey((x, y)))
						distances[(x, y)] = Math.Min(distances[(x, y)], distances[(prevX, prevY)] + 1);
					else
						distances[(x, y)] = distances.GetValueOrDefault((prevX, prevY), 0) + 1;
					break;
				}
			}

			(prevX, prevY) = (x, y);
		}

		return distances.Values.Count(dist => dist >= 1000).ToString();
	}
}