AdventOfCode/AdventOfCode.Solutions/2022/Day 09/RopeWalker.cs

namespace AdventOfCode.Solutions._2022.Day_09
{
    internal class VirtualPoint
    {
        internal int X { get; set; } = 0;

        internal int Y { get; set; } = 0;

        internal void Translate(int x, int y)
        {
            X += x;
            Y += y;
        }
    }

    internal class RopeWalker
    {
        private List<string> TailVistedLocations = new();

        internal int ProcessMovement(string[] movements, int ropeLength)
        {
            VirtualPoint[] rope = new VirtualPoint[ropeLength];
            for (int ropeIndex = 0; ropeIndex < rope.Length; ropeIndex++)
            {
                rope[ropeIndex] = new VirtualPoint();
            }

            // add the start position
            TailVistedLocations.Add($"0,0");

            for (int movementIndex = 0; movementIndex < movements.Length; movementIndex++)
            {
                char direction = movements[movementIndex][0];
                int amountToMove = Convert.ToInt32(movements[movementIndex].Substring(2));

                for (int movement = 0; movement < amountToMove; movement++)
                {

                    // do the actual move
                    switch (direction)
                    {
                        case 'U': rope[0].Translate(0, 1); break;
                        case 'D': rope[0].Translate(0, -1); break;
                        case 'R': rope[0].Translate(1, 0); break;
                        case 'L': rope[0].Translate(-1, 0); break;
                    }

                    for (int ropeIndex = 1; ropeIndex < rope.Length; ropeIndex++)
                    {
                        if (!IsTailTouchingHead(rope[ropeIndex - 1], rope[ropeIndex]))
                        {
                            rope[ropeIndex].Translate(Math.Sign(rope[ropeIndex - 1].X - rope[ropeIndex].X), Math.Sign(rope[ropeIndex - 1].Y - rope[ropeIndex].Y));

                            // add the new position to the list of visited positions
                            
                            continue;
                        }

                        // if not touching nothing has changed so stop with checking
                        break;
                    }

                    TailVistedLocations.Add($"{rope[^1].X},{rope[^1].Y}");
                }
            }

            return TailVistedLocations.Distinct().Count();
        }

        private bool IsTailTouchingHead(VirtualPoint point1, VirtualPoint point2)
        {
            return !(Math.Abs(point1.X - point2.X) > 1) && !(Math.Abs(point1.Y - point2.Y) > 1);
        }
    }
}