AdventOfCode/Days/Day12.cs

using Spectre.Console;

namespace AdventOfCode.Days;

public class Day12 : Day
{
    public override int Number => 12;
    public override string Name => "Hill Climbing Algorithm";

    public const int EndElevation = 25;

    // Color map of elevation: blue -> green -> yellow -> orange -> red
    private readonly Color[] _colorMap =
    {
        Color.Blue1,
        Color.DodgerBlue1,
        Color.DeepSkyBlue1,
        Color.Turquoise2,
        Color.Cyan1,
        Color.Cyan2,
        Color.MediumSpringGreen,
        Color.SpringGreen1,
        Color.SpringGreen2_1,
        Color.Green1,
        Color.DarkOliveGreen2,
        Color.GreenYellow,
        Color.DarkOliveGreen1,
        Color.Yellow2,
        Color.Khaki1,
        Color.Yellow1,
        Color.NavajoWhite1,
        Color.LightGoldenrod2_1,
        Color.Gold1,
        Color.SandyBrown,
        Color.Orange1,
        Color.DarkOrange,
        Color.OrangeRed1,
        Color.IndianRed1,
        Color.HotPink,
        Color.MediumOrchid1_1
    };

    private (int x, int y) _end;
    private (int x, int y) _start;

    public override void RunPart1(bool display = true)
    {
        var map = ParseMap();
        var canvas = DrawMap(map);

        // Test all possible solutions
        var minimumPathLength = ExplorePath(map);

        // Draw solution path
        foreach (var (x, y) in minimumPathLength.path)
        {
            canvas.SetPixel(x, y, Color.White);
        }

        if (display)
        {
            AnsiConsole.Write(canvas);
            AnsiConsole.WriteLine();

            AnsiConsole.MarkupLine($"[green]Minimum path length: [yellow]{minimumPathLength.length}[/][/]");
        }
    }

    public override void RunPart2(bool display = true)
    {
        var map = ParseMap();
        var canvas = DrawMap(map);

        // Test all possible solutions
        var minimumPathLength = FindNearestStart(map);

        // Draw solution path
        foreach (var (x, y) in minimumPathLength.path)
        {
            canvas.SetPixel(x, y, Color.White);
        }

        if (display)
        {
            AnsiConsole.Write(canvas);
            AnsiConsole.WriteLine();

            AnsiConsole.MarkupLine($"[green]Minimum path length: [yellow]{minimumPathLength.length}[/][/]");
        }
    }

    private (int length, List<(int x, int y)> path) ExplorePath(byte[,] map)
    {
        var height = map.GetLength(0);
        var width = map.GetLength(1);

        // Store seen positions with number of steps to reach this position
        var exploredPositions = new Dictionary<(int x, int y), int>();
        var toExplore = new Queue<(int x, int y, int elevation, int steps, List<(int x, int y)> path)>();
        var pathLengths = new List<(int length, List<(int x, int y)> path)>();

        toExplore.Enqueue((_start.x, _start.y, 0, 0, new()));

        // Explore all possible path
        while (toExplore.Count > 0)
        {
            var (x, y, previousElevation, steps, path) = toExplore.Dequeue();

            // If we went out of bound
            if (x < 0 || x >= width || y < 0 || y >= height)
            {
                continue;
            }

            // If new elevation is too high
            var newElevation = map[y, x];
            if (newElevation - previousElevation > 1)
            {
                continue;
            }

            // If new path is not better than old path, just skip
            if (exploredPositions.TryGetValue((x, y), out var oldSteps))
            {
                if (oldSteps <= steps)
                {
                    continue;
                }
            }

            // Mark this position as explored and store required number of steps to reach it
            exploredPositions[(x, y)] = steps;

            // Update path
            var newPath = new List<(int x, int y)>(path) { (x, y) };

            // If we found the end, note that we could end the search here since it's a bfs, there can't be
            // any shorter path to this point
            if ((x, y) == _end)
            {
                pathLengths.Add((steps, newPath));

                continue;
            }

            var nextPositions = new (int x, int y)[]
            {
                (x + 1, y), (x - 1, y), (x, y + 1), (x, y - 1)
            };

            foreach (var nextPosition in nextPositions)
            {
                toExplore.Enqueue((nextPosition.x, nextPosition.y, newElevation, steps + 1, newPath));
            }
        }

        return pathLengths.MinBy(p => p.length);
    }

    private (int length, List<(int x, int y)> path) FindNearestStart(byte[,] map)
    {
        var height = map.GetLength(0);
        var width = map.GetLength(1);

        // Store seen positions with number of steps to reach this position
        var exploredPositions = new Dictionary<(int x, int y), int>();
        var toExplore = new Queue<(int x, int y, int elevation, int steps, List<(int x, int y)> path)>();
        var pathLengths = new List<(int length, List<(int x, int y)> path)>();

        toExplore.Enqueue((_end.x, _end.y, EndElevation, 0, new()));

        // Explore all possible path
        while (toExplore.Count > 0)
        {
            var (x, y, previousElevation, steps, path) = toExplore.Dequeue();

            // If we went out of bound
            if (x < 0 || x >= width || y < 0 || y >= height)
            {
                continue;
            }

            // If new elevation is too low, skip
            var newElevation = map[y, x];
            if (previousElevation - newElevation > 1)
            {
                continue;
            }

            // If new path is not better than old path, just skip
            if (exploredPositions.TryGetValue((x, y), out var oldSteps))
            {
                if (oldSteps <= steps)
                {
                    continue;
                }
            }

            // Mark this position as explored and store required number of steps to reach it
            exploredPositions[(x, y)] = steps;

            // Update path
            var newPath = new List<(int x, int y)>(path) { (x, y) };

            // If we found a possible start, same as in the 1st part, we could stop here
            if (newElevation == 0)
            {
                pathLengths.Add((steps, newPath));

                continue;
            }

            var nextPositions = new (int x, int y)[]
            {
                (x + 1, y), (x - 1, y), (x, y + 1), (x, y - 1)
            };

            foreach (var nextPosition in nextPositions)
            {
                toExplore.Enqueue((nextPosition.x, nextPosition.y, newElevation, steps + 1, newPath));
            }
        }

        return pathLengths.MinBy(p => p.length);
    }

    private byte[,] ParseMap()
    {
        var lines = Input.ReadAllLines().ToArray();
        var lineCount = lines.Length;
        var columnCount = lines[0].Length;

        var map = new byte[lineCount, columnCount];

        for (int i = 0; i < lineCount; i++)
        {
            var line = lines[i];

            for (int j = 0; j < columnCount; j++)
            {
                var elevation = line[j];

                map[i, j] = elevation switch
                {
                    'S' => 0,
                    'E' => EndElevation,
                    _ => (byte) (elevation - 'a')
                };

                // Store the end
                if (elevation == 'E')
                {
                    _end = (j, i);
                }

                // Store the start
                if (elevation == 'S')
                {
                    _start = (j, i);
                }
            }
        }

        return map;
    }

    private Canvas DrawMap(byte[,] map)
    {
        var height = map.GetLength(0);
        var width = map.GetLength(1);

        var canvas = new Canvas(width, height);

        for (int x = 0; x < width; x++)
        {
            for (int y = 0; y < height; y++)
            {
                canvas.SetPixel(x, y, _colorMap[map[y, x]]);
            }
        }

        return canvas;
    }

    #region Input

    public const string Input =
    """
    abccccccaaccaaccccaaaaacccccaaaaccccccccccccccccccccccccccccccccaaaaaaaaaaaaaaaaaaaccccccccccccccccaaaccccccccccccaacccccccccccccccccccccccccccccccccccccccccaaaa
    abaaaaccaaaaaccccaaaaaccccccaaaaccccccccccccccccccccaaacccccccccccaaaaaaaaaaaaaaaaaaccccccccccccccccaaaaccccccaaacaaccccccccccccccccccccccccccccccccccccccccaaaaa
    abaaacccaaaaaaaacaaaaaacccccaaaaccccccccccccccccccccaaaaacccccccccaaaaaaaaaaaaaaaaacccccccccaaccccaaaaaacccccccaaaaaccccaaccccccccccccccacccccccccccccccccccaaaaa
    abaaacccccaaaaaccccaaaaccccccaaacccccccccccccccccccaaaaaccccccccccaaaaaacacaaaaaacccccccccccaaccccaaaaacccccccccaaaaaaccaaaaaaccccccccccaaaccccacccccccccccaaaaaa
    abaacccccaaaaaccccaacccccccccccccccaaaaacccccccccccaaaaacccccccccaaaaaaaaccaaaaaaacccccccaaaaaaaaccaaaaacccccccaaaaaaaccaaaaacccccccccccaaacccaaaccccccccccccccaa
    abaaacccaaacaacccccccccccccccccccccaaaaaccccccccccccaaaaacccccccaaaaaaaaaccaaccaaacccccccaaaaaaaaccaacccccccccaaaaaaccaaaaaaccccccccccccaaaacaaaaccccccccccccccaa
    abaaacccccccaaccccccccccccccccccccaaaaaaccccccccccccaaccccccaacccaaaccaaaaccccccaacccccccccaaaacccccccccccccccaacaaaccaaaaaaaccccccccccccajjjjjjjcccccccccccccccc
    abcaacccccccccccccccccccccccccccccaaaaaaccccccccccccccccccccaaaaccccccaaaaccccccccccccccaacaaaaaccccccccccccccccccaaccccaaaaaacccccccccccjjjjjjjjjcccccaaaccccccc
    abccccccccccccccccccccccccccccccccaaaaaaccaaccccccccccccccaaaaaacccccccaaacccccccccccaacaaaaaaaaccccccccccccccccccccccccaaccaaccccccccaiijjjjojjjjcccccaaacaccccc
    abcccccccccccccccccccccccaaacccccccaaacacaaacccccccccccccccaaaaccccaaccccccccccccccccaaaaaaacccaccccccccccccccccccccccccaacccccccccccaiiijjooooojjkccaaaaaaaacccc
    abccccccccccccccccccccccaaaaccccccccccaaaaaccccccccccccccccaaaaacccaaaaaccccccccccccccaaaaaacccccccccccccccccccccccccccccccccccccciiiiiiiioooooookkkcaaaaaaaacccc
    abccccccccccccccccccccccaaaaccccccccccaaaaaaaacccccccccccccaacaaccaaaaacccccccaaacccaaaaaaaaccccccccccccccccccccccccccccccccccchiiiiiiiiooooouoookkkccaaaaaaccccc
    abcccccccccaaccccccccccccaaaccccccccccccaaaaacccccccccccccccccccccaaaaaccccccaaaacccaaaaacaacccccccccccccaacaacccccccccccccccchhhiiiinnnooouuuuoookkkccaaaaaccccc
    abcccccccccaaacccccccccccccccccccccccccaaaaacccccccccccccccccccccccaaaaacccccaaaaccccccaaccccccccccccccccaaaaacccccccccccccccchhhnnnnnnnnouuuuuuppkkkkaaaaaaccccc
    abccccccaaaaaaaacccaaccccccccccccccccccaacaaccaacaaccccccccccccccccaacccccccccaaaccccccaacccccccccccccccaaaaacccccccccccccccchhhnnnnnnnnntuuxuuupppkkkkkacccccccc
    abccccccaaaaaaaacacaaaacccccccccccccccccccaaccaaaaacccccccccccccccccccccccccccccccccccccccccccccccccccccaaaaaacccccccaacccccchhhnnnnttttttuxxxuuppppkkkkkcccccccc
    abcccccccaaaaaaccaaaaaaccccccccccaaccccccccccaaaaaccccccccccccccccccccccccaaacccccccccccccccccccccccccccccaaaaccaaccaaacccaaahhhnnntttttttuxxxxuupppppllllccccccc
    abcccccccaaaaaacccaaaacccccccccaaaaaaccccccccaaaaaacccccccccccccccccccccccaaacccccccccccccccccccccccccccccacccccaaaaaaacaaaaahhhppntttxxxxxxxxuuuuvpppplllccccccc
    abcccccccaaaaaacccaaaacccccccccaaaaaacccccaaaaaaaaaccccccccccccccccccccaaaaaaaacccccccccccccccccccccaaaccccccaacaaaaaaccaaaaahhhpppttxxxxxxxxyuuvvvvvppplllcccccc
    abcccccccaaccaacccaacaccaaaaccccaaaaacccccaaaaaaaaaccccccccccccccccccccaaaaaaaacccccccccccccccccccccaaacaaaaaaaccaaaaaaaaaaaaahhppptttxxxxxxyyyyyyvvvppplllcccccc
    SbccccccccccccccccccccccaaaacccaaaaacccccccaaaaaaaaacaaaccccccccaacccccccaaaaaccccccccaaaaacccccccccaaaaaaaaaaaaaaaaaaaaaaaaacgggpppttxxxxEzzyyyyyvvvqqqlllcccccc
    abccccccccccccccccccccccaaaacccaaaaacccccccaaaaaaaaccaaaccccccccaaacaaccaaaaaaccccccccaaaaacccccccaaaaaaaaaaaaaaaaaaaaaaaaaaacgggpppsssxxxyyyyyyvvvvvqqlllccccccc
    abcccaaaccccccccccccccccaaaccccccccccccccccaaaaaaaaaaaaaccccccccaaaaaaccaaaaaacccccccaaaaaacccaaaccaaaaaccaaaaaaaaaaaacccccccccgggppssswwyyyyyyvvvvqqqqlllccccccc
    abcaaaaaccccccccccccccccccccccccccccccccccaaaaaaaaaaaaacccccccaaaaaaacccaccaaacccccccaaaaaacccaaacccaaaaaaaaaaaccccaaacccaaaaacgggppsswwwyyyyyyvvqqqqqlllcccccccc
    abcaaaaaaccccccccccccccccccccccccccccccccccaaccaaaaaaaaaaaccccaaaaaaacccccccccccccccccaaaaacccaaacaaaacaaaaaaaaccccaaacccaaaaacggpppsswwwywwyyyvvqqqmmmlccccccccc
    abcaaaaaacccccccaacaaccccccccccccccccccccccccccaaaaaaaaaaaccccccaaaaacccccccccccccccccaaaccaaaaaaaaaaacccccccaacccccccccaaaaaacggpppsswwwwwwwwyvvqqqmmmcccccccccc
    abcaaaaaccccccccaaaaaccccccccccccccccccccccccccccaaaaaaaacccccccaacaaacccccccccccccccccccccaaaaaaaaaccccccccccccccccccccaaaaaagggoossswwwwrrwwwvvqqmmmccccccccccc
    abcaaaaacccccccaaaaaccccccccccccccccccccccccccccaaaaaaacccccccccaaccccccccccccccccccccccccccaaaaaaacccccccccccaaaccccccccaaaaagggooosssssrrrrwwwvqqmmmcccaacccccc
    abcccccccccccccaaaaaaccccccccccccccccccccaacccccccccaaaccccccccccccccccccccccccccccccccccccccaaaaaaccccccccccccaaaaccccccaaaccgggooosssssrrrrrwwrrqmmmcccaacccccc
    abcccccccccccccccaaaacccccccccccccccccccaaaacccccccacaaacccccccccccccccccccccccccccccccccccccaaaaaaacccccccccaaaaaacccccccccccgffoooooosoonrrrrrrrrmmmccaaaaacccc
    abcccccccccccccccaccccccccccccccccccccccaaaacccccccaaaaacccccccccccccccccccccccccccccccccccccaaacaaacccccccccaaaaacccccccccccccfffoooooooonnnrrrrrmmmddcaaaaacccc
    abccccccccccccccccccccccccccccccccccccccaaaaccccccccaaaaacccccccccccccccccccccccccaaaccccccccaacccccccccccccccaaaaaccccccccccccffffoooooonnnnnnrnnmmmdddaaaaacccc
    abcccccccccccccccccccccccccccccccccccccccccccccccccaaaaaacccccccccccccccccaaaaaccaaaacccccccccccccccccccccccccaacccccccccccccccfffffffffeeeennnnnnmmdddaaaacccccc
    abcccccccaaaccccccccaccccccccccccccccccccccccccccccaaaaccccccccccccaaaccccaaaaaccaaaaccccccccccccccccccccccccccccccccccccccccccccfffffffeeeeennnnnmddddaaaaaccccc
    abcccaaccaaacccccaaaacccccaacccccccccccccccccccccccccaaacccccccccccaaacccaaaaaacccaaaccccccccccccccccccccccccccccccccccccccccccccccffffeeeeeeeedddddddcccaacccccc
    abcccaaaaaaacccccaaaaaaccaaacccccccccccccccccccccccccccacccccccccccaaaaccaaaaaaccccccccccccccccccccccccccaacccccccccaaaccccccccccccccaaaaaaeeeeedddddcccccccccccc
    abcccaaaaaacccccccaaaacccaaacaaaccccaaaacccccccccaaacaaaccccccaacccaaaacaaaaaaacccccccccccccccccccccccccaaaccccccccaaaacccccccccccccccccccaaaaeeddddccccccccccccc
    abccccaaaaaaaacccaaaaaaaaaaaaaaaccccaaaacccccccccaaaaaaacccccaaacccaaaaaaaaaacccccccccccccccccccccccaaacaaaccccccccaaaaccccccccccccccccccccaaaccccccccccccccaaaca
    abcccaaaaaaaaacccaacaaaaaaaaaaacccccaaaaccccccccccaaaaaacaaacaaacaaaaaaaaaacccccccccccccccaaacccccccaaaaaaaaaaccccccaaaccccccccccccccccccccaacccccccccccccccaaaaa
    abcccaaaaaaaacccccccccccaaaaaacccccccaacccccccccccaaaaaaaaaaaaaaaaaaaaaaaaccccccccccccccccaaaacccccccaaaaaaaaacccccccccccccccccccccccccccccaaacccccccccccccccaaaa
    abccaaaaaaacccccccccccccaaaaaaacccccccccccccccccaaaaaaaaaaaaaaaaaaaaaaaaaaacccccccccccccccaaaacccccccaaaaaaaacccccccccccccccccccccccccccccccccccccccccccccccaaaaa
    """;

    #endregion
}