init current

day09/day09/Problem.cs

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+namespace day09;
+public class Problem
+{
+    public string Result1 { get; set; }
+    public string Result2 { get; set; }
+
+    public void ResolvePart1(string arg)
+    {
+        var lines = File.ReadAllLines(arg);
+
+        var tailPositions = new HashSet<(int, int)>();
+        tailPositions.Add((0, 0));//start position
+        var currentHeadPos = (x: 0, y: 0);
+        var knots = new List<(int x, int y)>();
+        // nr of knots
+        // PART 1
+        var knotsNo = 1;
+        knots.Add(currentHeadPos);
+        for (int i = 0; i < knotsNo; i++)
+        {
+            knots.Add((0, 0));
+        }
+        foreach (var line in lines)
+        {
+            var linecmd = line.Split(" ");
+            var direction = linecmd[0];
+            var tiles = int.Parse(linecmd[1]);
+            // System.Console.WriteLine($"{direction} {tiles}");
+            for (int i = 0; i < tiles; i++)
+            {
+                switch (direction)
+                {
+                    case "U":
+                        currentHeadPos = (currentHeadPos.x, currentHeadPos.y - 1);
+                        break;
+                    case "D":
+                        currentHeadPos = (currentHeadPos.x, currentHeadPos.y + 1);
+                        break;
+                    case "L":
+                        currentHeadPos = (currentHeadPos.x - 1, currentHeadPos.y);
+                        break;
+                    case "R":
+                        currentHeadPos = (currentHeadPos.x + 1, currentHeadPos.y);
+                        break;
+                    default:
+                        throw new ArgumentException($"command {direction} not supported", nameof(direction));
+                }
+                knots[0] = currentHeadPos;
+
+                for (int j = 0; j < knotsNo; j++)
+                {
+                    var firstKnot = knots[j];
+                    var secondKnot = knots[j + 1];
+                    AdjustTailPos(ref firstKnot, ref secondKnot);
+                    knots[j + 1] = secondKnot;
+                }
+                tailPositions.Add(knots.Last());//add tail pos
+            }
+        }
+        // get # of unique positions visited by the tail - T
+        // System.Console.WriteLine($"tail visited positions {tailPositions.Count}");
+        // P1
+        //5710
+
+        Result1 = tailPositions.Count.ToString();
+    }
+
+    public void ResolvePart2(string arg)
+    {
+        var lines = File.ReadAllLines(arg);
+
+        var tailPositions = new HashSet<(int, int)>();
+        tailPositions.Add((0, 0));//start position
+        var currentHeadPos = (x: 0, y: 0);
+        var knots = new List<(int x, int y)>();
+        // nr of knots
+        //PART2
+        var knotsNo = 9;
+        knots.Add(currentHeadPos);
+        for (int i = 0; i < knotsNo; i++)
+        {
+            knots.Add((0, 0));
+        }
+        foreach (var line in lines)
+        {
+            var linecmd = line.Split(" ");
+            var direction = linecmd[0];
+            var tiles = int.Parse(linecmd[1]);
+            // System.Console.WriteLine($"{direction} {tiles}");
+            for (int i = 0; i < tiles; i++)
+            {
+                switch (direction)
+                {
+                    case "U":
+                        currentHeadPos = (currentHeadPos.x, currentHeadPos.y - 1);
+                        break;
+                    case "D":
+                        currentHeadPos = (currentHeadPos.x, currentHeadPos.y + 1);
+                        break;
+                    case "L":
+                        currentHeadPos = (currentHeadPos.x - 1, currentHeadPos.y);
+                        break;
+                    case "R":
+                        currentHeadPos = (currentHeadPos.x + 1, currentHeadPos.y);
+                        break;
+                    default:
+                        throw new ArgumentException($"command {direction} not supported", nameof(direction));
+                }
+                knots[0] = currentHeadPos;
+
+                for (int j = 0; j < knotsNo; j++)
+                {
+                    var firstKnot = knots[j];
+                    var secondKnot = knots[j + 1];
+                    AdjustTailPos(ref firstKnot, ref secondKnot);
+                    knots[j + 1] = secondKnot;
+                }
+                tailPositions.Add(knots.Last());//add tail pos
+            }
+        }
+        // get # of unique positions visited by the tail - T
+        // System.Console.WriteLine($"tail visited positions {tailPositions.Count}");
+        // P2
+        //2259
+
+        Result2 = tailPositions.Count.ToString();
+    }
+
+    public static void AdjustTailPos(ref (int x, int y) headPos, ref (int x, int y) tailPos)
+    {
+        var dX = headPos.x - tailPos.x;
+        var dY = headPos.y - tailPos.y;
+        if (Math.Abs(dX) > 1 || Math.Abs(dY) > 1)
+        {
+            if (Math.Abs(dX) * Math.Abs(dY) > 1)
+            {
+                //diagonal
+                tailPos = (
+                    tailPos.x + Math.Sign(dX),
+                    tailPos.y + Math.Sign(dY)
+                );
+            }
+            else
+            {
+                tailPos = (
+                    tailPos.x + (Math.Abs(dX) > 0 ? (dX - Math.Sign(dX) * 1) : 0),
+                    tailPos.y + (Math.Abs(dY) > 0 ? (dY - Math.Sign(dY) * 1) : 0)
+                );
+            }
+        }
+    }
+}

day09/day09/Program.cs

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+namespace day09;
+class Program
+{
+    static void Main(string[] args)
+    {
+        var inputFile = "input.txt";
+
+        var problem = new Problem();
+
+        problem.ResolvePart1(inputFile);
+        System.Console.WriteLine($"Result1: {problem.Result1}");
+
+        problem.ResolvePart2(inputFile);
+        System.Console.WriteLine($"Result2: {problem.Result2}");
+    }
+}

day09/day09/day09.csproj

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+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net6.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+</Project>