Day 9.txt

    internal class Program
    {
        static void Main(string[] args)
        {
            string[] input = File.ReadAllLines(@"C:/Users/pette/Documents/AoC9.txt");
            List<Action> actionList = new List<Action>();
            foreach (string s in input)
            {
                actionList.Add(new Action(s[0], Convert.ToInt32(s[2..])));
            }

            // Create all 10 knots
            RopeEnd H = new RopeEnd(0, 0);
            RopeEnd a1 = new RopeEnd(0, 0);
            RopeEnd a2 = new RopeEnd(0, 0);
            RopeEnd a3 = new RopeEnd(0, 0);
            RopeEnd a4 = new RopeEnd(0, 0);
            RopeEnd a5 = new RopeEnd(0, 0);
            RopeEnd a6 = new RopeEnd(0, 0);
            RopeEnd a7 = new RopeEnd(0, 0);
            RopeEnd a8 = new RopeEnd(0, 0);
            RopeEnd a9 = new RopeEnd(0, 0);

            // Loop through actions.
            foreach (Action a in actionList)
            {
                // One step at a time, check positions and adjust according
                // to instructions for every knot.
                for (int i = 0; i < a.steps; i++)
                {
                    H = RopeEnd.MoveHead(H, a.dir);
                    a1 = RopeEnd.CheckKnot(H, a1);
                    a2 = RopeEnd.CheckKnot(a1, a2);
                    a3 = RopeEnd.CheckKnot(a2, a3);
                    a4 = RopeEnd.CheckKnot(a3, a4);
                    a5 = RopeEnd.CheckKnot(a4, a5);
                    a6 = RopeEnd.CheckKnot(a5, a6);
                    a7 = RopeEnd.CheckKnot(a6, a7);
                    a8 = RopeEnd.CheckKnot(a7, a8);
                    a9 = RopeEnd.CheckKnot(a8, a9);
                    // Check tails position and update list if it's a new coordinate
                    if (!RopeEnd.FindFootprint(a9))
                    {
                        RopeEnd.AddToList(a9);
                    }
                }
            }

            // Print out total coordinates visited.
            Console.WriteLine(RopeEnd.footPrints.Count);
        }
    }

    public class Action
    {
        public int steps;
        public char dir;

        public Action(char dir, int steps)
        {
            this.steps = steps;
            this.dir = dir;
        }
    }

    public class RopeEnd
    {
        public int x;
        public int y;

        public RopeEnd(int x, int y)
        {
            this.x = x;
            this.y = y;
        }

        // Create list of positions and add starting point as first entry
        public static List<Tuple<int, int>> footPrints = new List<Tuple<int, int>>() { Tuple.Create<int, int>(0, 0) };

        // Moves the head one step in ordered direction
        public static RopeEnd MoveHead(RopeEnd A, char dir)
        {
            if (dir == 'U')
            {
                A.x++;
            }
            else if (dir == 'D')
            {
                A.x--;
            }
            else if (dir == 'R')
            {
                A.y++;
            }
            else if (dir == 'L')
            {
                A.y--;
            }
            return A;
        }

        // Checks if current knot is too far away from previous and moves if it is.
        public static RopeEnd CheckKnot(RopeEnd A, RopeEnd B)
        {
            // If previous knot is more than one step above current.
            if (A.x - B.x > 1)
            {
                if (A.y == B.y)
                {
                    B.x++;
                }
                else if (A.y > B.y)
                {
                    B.x++;
                    B.y++;
                }
                else if (A.y < B.y)
                {
                    B.x++;
                    B.y--;
                }
            }
            // If head is more than one step below tail
            else if (A.x - B.x < -1)
            {
                if (A.y == B.y)
                {
                    B.x--;
                }
                else if (A.y > B.y)
                {
                    B.x--;
                    B.y++;
                }
                else if (A.y < B.y)
                {
                    B.x--;
                    B.y--;
                }

            }
            // If head is more than one step to the right of tail
            if (A.y - B.y > 1)
            {
                if (A.x == B.x)
                {
                    B.y++;
                }
                else if (A.x > B.x)
                {
                    B.y++;
                    B.x++;
                }
                else if (A.x < B.x)
                {
                    B.y++;
                    B.x--;
                }
            }
            // If head is more than one step to the left of tail
            if (A.y - B.y < -1)
            {
                if (A.x == B.x)
                {
                    B.y--;
                }
                else if (A.x > B.x)
                {
                    B.y--;
                    B.x++;
                }
                else if (A.x < B.x)
                {
                    B.y--;
                    B.x--;
                }
            }
            return B;
        }

        public static void AddToList(RopeEnd A)
        {
            footPrints.Add(Tuple.Create(A.x, A.y));
        }

        // Checks if current position has been registered.
        public static bool FindFootprint(RopeEnd A)
        {
            foreach (Tuple<int, int> t in footPrints)
            {
                if (t.Item1 == A.x && t.Item2 == A.y)
                {
                    return true;
                }
            }
            return false;
        }
    }