AdventOfCode/Advent Of Code Library/2022/Day 09/RopeWalker.cs

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

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

        internal void MoveUp()
        {
            Y++;
        }

        internal void MoveDown()
        {
            Y--;
        }

        internal void MoveRight()
        {
            X++;
        }

        internal void MoveLeft()
        {
            X--;
        }
    }

    internal class RopeWalker
    {
        private VirtualPoint HeadLocation = new();
        private VirtualPoint LastHeadLocation = new();

        private VirtualPoint TailLocation = new();

        private List<string> TailVistedLocations = new();

        internal int ProcessMovement(string[] movements)
        {
            // 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++)
                {
                    // set the last pos before moving
                    LastHeadLocation = HeadLocation;

                    // do the actual move
                    switch (direction)
                    {
                        case 'U': HeadLocation.MoveUp(); break;
                        case 'D': HeadLocation.MoveDown(); break;
                        case 'R': HeadLocation.MoveRight(); break;
                        case 'L': HeadLocation.MoveLeft(); break;
                    }

                    // check if the tail is touching
                    if (!IsTailTouchingHead(direction))
                    {
                        // if not, move tail to last head position
                        TailLocation = LastHeadLocation;

                        // add the new position to the list of visited positions
                        TailVistedLocations.Add($"{TailLocation.X},{TailLocation.Y}");
                    }
                }
            }

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

        private bool IsTailTouchingHead(char direction)
        {
            return direction switch
            {
                // up; Y + 1
                'U' => TailLocation.Y + 1 >= HeadLocation.Y,
                // down; Y - 1
                'D' => TailLocation.Y - 1 <= HeadLocation.Y,
                // right; X + 1
                'R' => TailLocation.X + 1 >= HeadLocation.X,
                // left; X - 1
                'L' => TailLocation.X - 1 <= HeadLocation.X,
                _ => throw new AccessViolationException(),
            };
        }
    }
}