Day 21

MartinZikmund · Feb 11, 2024 · 654b274 · 654b274
1 parent f48d30d
commit 654b274
Show file tree

Hide file tree

Showing 11 changed files with 508 additions and 0 deletions.
diff --git a/AdventOfCode.sln b/AdventOfCode.sln
@@ -85,6 +85,10 @@ Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Day20_1", "Day20_1\Day20_1.
 EndProject
 Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Day20_2", "Day20_2\Day20_2.csproj", "{3CB2C32D-2326-4FAE-9D34-56DDC1C2A463}"
 EndProject
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Day21_1", "Day21_1\Day21_1.csproj", "{A39616AE-A2EF-4B33-933C-2A2D6104F32E}"
+EndProject
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Day21_2", "Day21_2\Day21_2.csproj", "{AC399EF1-B2BE-4089-8F96-EC503D79CC77}"
+EndProject
 Global
 	GlobalSection(SolutionConfigurationPlatforms) = preSolution
 		Debug|Any CPU = Debug|Any CPU
@@ -255,6 +259,14 @@ Global
 		{3CB2C32D-2326-4FAE-9D34-56DDC1C2A463}.Debug|Any CPU.Build.0 = Debug|Any CPU
 		{3CB2C32D-2326-4FAE-9D34-56DDC1C2A463}.Release|Any CPU.ActiveCfg = Release|Any CPU
 		{3CB2C32D-2326-4FAE-9D34-56DDC1C2A463}.Release|Any CPU.Build.0 = Release|Any CPU
+		{A39616AE-A2EF-4B33-933C-2A2D6104F32E}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{A39616AE-A2EF-4B33-933C-2A2D6104F32E}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{A39616AE-A2EF-4B33-933C-2A2D6104F32E}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{A39616AE-A2EF-4B33-933C-2A2D6104F32E}.Release|Any CPU.Build.0 = Release|Any CPU
+		{AC399EF1-B2BE-4089-8F96-EC503D79CC77}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{AC399EF1-B2BE-4089-8F96-EC503D79CC77}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{AC399EF1-B2BE-4089-8F96-EC503D79CC77}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{AC399EF1-B2BE-4089-8F96-EC503D79CC77}.Release|Any CPU.Build.0 = Release|Any CPU
 	EndGlobalSection
 	GlobalSection(SolutionProperties) = preSolution
 		HideSolutionNode = FALSE

diff --git a/Day21_1/Day21_1.csproj b/Day21_1/Day21_1.csproj
@@ -0,0 +1,24 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net8.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <None Remove="input.txt" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <Content Include="input.txt">
+      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
+    </Content>
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\Tools\Tools.csproj" />
+  </ItemGroup>
+
+</Project>
diff --git a/Day21_1/Program.cs b/Day21_1/Program.cs
@@ -0,0 +1,67 @@
+using Tools;
+
+const char Empty = '.';
+const char Occupied = '#';
+const char Start = 'S';
+
+var input = File.ReadAllLines("input.txt");
+var width = input[0].Length;
+var height = input.Length;
+Point startPosition = default;
+var map = new char[width, height];
+for (var y = 0; y < height; y++)
+{
+    for (var x = 0; x < width; x++)
+    {   
+        map[x, y] = input[y][x];
+        if (input[y][x] == Start)
+        {
+            startPosition = new Point(x, y);
+            map[x, y] = Empty;
+        }
+    }
+}
+
+var result = CalculateReachable(startPosition, 1000);
+Console.WriteLine(result);
+
+long CalculateReachable(Point startPosition, int steps)
+{
+    HashSet<Point> visited = new();
+    HashSet<Point> reachable = new();
+    Queue<(Point Position, int CurrentSteps)> queue = new();
+    queue.Enqueue((startPosition, 0));
+    visited.Add(startPosition);
+
+    while (queue.Count > 0)
+    {
+        var (position, currentSteps) = queue.Dequeue();
+
+        if (steps % 2 == currentSteps % 2)
+        {
+            reachable.Add(position);
+        }
+
+        if (currentSteps == steps)
+        {
+            continue;
+        }
+
+        foreach (var direction in Directions.WithoutDiagonals)
+        {
+            var newPosition = position + direction;
+            if (newPosition.X < 0 || newPosition.X >= width || newPosition.Y < 0 || newPosition.Y >= height)
+            {
+                continue;
+            }
+
+            if (map[newPosition.X, newPosition.Y] == Empty && !visited.Contains(newPosition))
+            {                
+                visited.Add(newPosition);
+                queue.Enqueue((newPosition, currentSteps + 1));
+            }
+        }
+    }
+
+    return reachable.Count;
+}
diff --git a/Day21_1/Properties/launchSettings.json b/Day21_1/Properties/launchSettings.json
@@ -0,0 +1,7 @@
+{
+  "profiles": {
+    "Run": {
+      "commandName": "Project"
+    }
+  }
+}
diff --git a/Day21_1/input.txt b/Day21_1/input.txt
diff --git a/Day21_1/output.txt b/Day21_1/output.txt
diff --git a/Day21_2/Day21_2.csproj b/Day21_2/Day21_2.csproj
@@ -0,0 +1,24 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net8.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <None Remove="input.txt" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <Content Include="input.txt">
+      <CopyToOutputDirectory>PreserveNewest</CopyToOutputDirectory>
+    </Content>
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\Tools\Tools.csproj" />
+  </ItemGroup>
+
+</Project>
diff --git a/Day21_2/Program.cs b/Day21_2/Program.cs
@@ -0,0 +1,105 @@
+using Tools;
+
+const char Empty = '.';
+const char Occupied = '#';
+const char Start = 'S';
+
+const long TotalSteps = 26501365;
+
+var input = File.ReadAllLines("input.txt");
+var mapSize = input[0].Length;
+Point startPosition = default;
+var map = new char[mapSize, mapSize];
+for (var y = 0; y < mapSize; y++)
+{
+    for (var x = 0; x < mapSize; x++)
+    {
+        map[x, y] = input[y][x];
+        if (input[y][x] == Start)
+        {
+            startPosition = new Point(x, y);
+            map[x, y] = Empty;
+        }
+    }
+}
+
+checked
+{
+    var oddMapStepCount = CalculateReachable(startPosition, 10017);
+    var evenMapStepCount = CalculateReachable(startPosition, 10020);
+
+    long farthestMap = (TotalSteps - mapSize / 2) / (mapSize);
+    var evenFullMapCount = farthestMap * farthestMap;
+    var oddFullMapCount = (farthestMap - 1) * (farthestMap - 1);
+
+    var oddStepsFull = oddFullMapCount * oddMapStepCount;
+    var evenStepsFull = evenFullMapCount * evenMapStepCount;
+
+    int smallTriangleSteps = (int)(TotalSteps - ((mapSize / 2) + (farthestMap - 1) * mapSize + (mapSize / 2) + 2));
+    var smallTriangleTopRightReachable = CalculateReachable(new Point(0, mapSize - 1), smallTriangleSteps);
+    var smallTriangleTopLeftReachable = CalculateReachable(new Point(mapSize - 1, mapSize - 1), smallTriangleSteps);
+    var smallTriangleBottomRightReachable = CalculateReachable(new Point(0, 0), smallTriangleSteps);
+    var smallTriangleBottomLeftReachable = CalculateReachable(new Point(mapSize - 1, 0), smallTriangleSteps);
+
+    var smallTriangleStepsFull = (smallTriangleTopRightReachable + smallTriangleTopLeftReachable + smallTriangleBottomRightReachable + smallTriangleBottomLeftReachable) * farthestMap;
+
+    int largeTriangleSteps = (int)(TotalSteps - ((mapSize / 2) + (farthestMap - 2) * mapSize + (mapSize / 2) + 2));
+    var largeTriangleTopRightReachable = CalculateReachable(new Point(0, mapSize - 1), largeTriangleSteps);
+    var largeTriangleTopLeftReachable = CalculateReachable(new Point(mapSize - 1, mapSize - 1), largeTriangleSteps);
+    var largeTriangleBottomRightReachable = CalculateReachable(new Point(0, 0), largeTriangleSteps);
+    var largeTriangleBottomLeftReachable = CalculateReachable(new Point(mapSize - 1, 0), largeTriangleSteps);
+
+    var largeTriangleStepsFull = (largeTriangleTopRightReachable + largeTriangleTopLeftReachable + largeTriangleBottomRightReachable + largeTriangleBottomLeftReachable) * (farthestMap - 1);
+
+    var edgeSteps = (int)(TotalSteps - ((mapSize / 2) + (farthestMap - 1) * mapSize + 1));
+    var edgeTopReachable = CalculateReachable(new Point(mapSize / 2, mapSize - 1), edgeSteps);
+    var edgeLeftReachable = CalculateReachable(new Point(mapSize - 1, mapSize / 2), edgeSteps);
+    var edgeBottomReachable = CalculateReachable(new Point(mapSize / 2, 0), edgeSteps);
+    var edgeRightReachable = CalculateReachable(new Point(0, mapSize / 2), edgeSteps);
+
+    var edgeStepsFull = edgeTopReachable + edgeLeftReachable + edgeBottomReachable + edgeRightReachable;
+
+    var result = oddStepsFull + evenStepsFull + smallTriangleStepsFull + largeTriangleStepsFull + edgeStepsFull;
+    Console.WriteLine(result);
+}
+
+long CalculateReachable(Point startPosition, int steps)
+{
+    HashSet<Point> visited = new();
+    HashSet<Point> reachable = new();
+    Queue<(Point Position, int CurrentSteps)> queue = new();
+    queue.Enqueue((startPosition, 0));
+    visited.Add(startPosition);
+
+    while (queue.Count > 0)
+    {
+        var (position, currentSteps) = queue.Dequeue();
+
+        if (steps % 2 == currentSteps % 2)
+        {
+            reachable.Add(position);
+        }
+
+        if (currentSteps == steps)
+        {
+            continue;
+        }
+
+        foreach (var direction in Directions.WithoutDiagonals)
+        {
+            var newPosition = position + direction;
+            if (newPosition.X < 0 || newPosition.X >= mapSize || newPosition.Y < 0 || newPosition.Y >= mapSize)
+            {
+                continue;
+            }
+
+            if (map[newPosition.X, newPosition.Y] == Empty && !visited.Contains(newPosition))
+            {
+                visited.Add(newPosition);
+                queue.Enqueue((newPosition, currentSteps + 1));
+            }
+        }
+    }
+
+    return reachable.Count;
+}
diff --git a/Day21_2/Properties/launchSettings.json b/Day21_2/Properties/launchSettings.json
@@ -0,0 +1,7 @@
+{
+  "profiles": {
+    "Run": {
+      "commandName": "Project"
+    }
+  }
+}