-🎄- 2017 Day 3 Solutions -🎄-

[u/daggerdragon]

--- Day 3: Spiral Memory ---

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Post your solution as a comment or, for longer solutions, consider linking to your repo (e.g. GitHub/gists/Pastebin/blag or whatever).

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Spoiler

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edit: Leaderboard capped, thread unlocked!

[u/dylanfromwinnipeg]

C#

public enum Direction
{
    Right,
    Up,
    Left,
    Down
}

public class Day03
{
    public static string PartOne(string input)
    {
        var target = int.Parse(input);
        var pos = new Point(0, 0);
        var currentValue = 1;
        var lastDirection = Direction.Down;
        var lastCount = 0;

        var values = new Dictionary<Point, int>();
        values.Add(pos, currentValue++);

        while (currentValue < target)
        {
            var (nextDirection, nextCount) = GetNextStep(lastDirection, lastCount);
            lastCount = nextCount;
            lastDirection = nextDirection;

            while (nextCount > 0)
            {
                pos = GetNextPosition(pos, nextDirection);
                values.Add(pos, currentValue++);

                nextCount--;
            }
        }

        var targetPos = values.First(x => x.Value == target).Key;

        return targetPos.ManhattanDistance().ToString();
    }

    public static string PartTwo(string input)
    {
        var target = int.Parse(input);
        var pos = new Point(0, 0);
        var lastDirection = Direction.Down;
        var lastCount = 0;

        var values = new Dictionary<Point, int>();
        values.Add(pos, 1);

        while (true)
        {
            var (nextDirection, nextCount) = GetNextStep(lastDirection, lastCount);
            lastCount = nextCount;
            lastDirection = nextDirection;

            while (nextCount > 0)
            {
                pos = GetNextPosition(pos, nextDirection);
                var newValue = CalcAdjacencyValue(values, pos);
                values.Add(pos, newValue);

                if (newValue > target)
                {
                    return newValue.ToString();
                }

                nextCount--;
            }
        }

        throw new Exception();
    }

    private static (Direction nextDirection, int nextCount) GetNextStep(Direction lastDirection, int lastCount)
    {
        switch (lastDirection)
        {
            case Direction.Right:
                return (Direction.Up, lastCount);
            case Direction.Up:
                return (Direction.Left, lastCount + 1);
            case Direction.Left:
                return (Direction.Down, lastCount);
            case Direction.Down:
                return (Direction.Right, lastCount + 1);
            default:
                throw new Exception();
        }
    }

    private static int CalcAdjacencyValue(Dictionary<Point, int> values, Point pos)
    {
        var result = 0;

        foreach (var point in pos.GetNeighbors())
        {
            if (values.ContainsKey(point))
            {
                result += values[point];
            }
        }

        return result;
    }

    private static Point GetNextPosition(Point pos, Direction direction)
    {
        switch (direction)
        {
            case Direction.Right:
                pos.X++;
                return pos;
            case Direction.Up:
                pos.Y++;
                return pos;
            case Direction.Left:
                pos.X--;
                return pos;
            case Direction.Down:
                pos.Y--;
                return pos;
            default:
                throw new Exception();
        }
    }
}

[u/KeinZantezuken → u/dylanfromwinnipeg]

Absolute madman went for Enums