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feat(2024-06): Add day 6 part 1 with some work towards part 2
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Josh Creek
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using AOC.Tests.Helpers;
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namespace AOC.Tests.Y2024;
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[TestFixture]
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[Parallelizable(ParallelScope.All)]
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public class Day06
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{
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[SetUp]
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public void Setup()
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{
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realData = File.ReadAllLines(Path.Combine(TestContext.CurrentContext.TestDirectory, "Y2024", "Data",
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$"{GetThisClassName()}.dat"));
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}
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protected string GetThisClassName() { return GetType().Name; }
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private string[] realData;
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private void TraverseGridAsGuard(ref char[,] grid, ref List<string> possibleExtraLoops)
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{
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// Traverse the grid as the guard, marking each cell as visited with an X
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// ^ means guard facing up, > means guard facing right, v means guard facing down, < means guard facing left
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// Find the guard
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int guardRow = -1;
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int guardCol = -1;
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for (int r = 0; r < grid.GetLength(0); r++)
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{
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for (int c = 0; c < grid.GetLength(1); c++)
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{
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if (grid[r, c] == '^' || grid[r, c] == '>' || grid[r, c] == 'v' || grid[r, c] == '<')
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{
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guardRow = r;
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guardCol = c;
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break;
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}
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}
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if (guardRow != -1)
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{
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break;
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}
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}
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// Record the direction the guard is facing
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char guardDirection = grid[guardRow, guardCol];
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// Mark the initial cell as visited
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grid[guardRow, guardCol] = 'X';
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Console.WriteLine($"{guardCol},{guardRow} {guardDirection}");
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// int tempCounter = 0;
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// While the guard is still on the grid
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while (guardRow >= 0 && guardRow < grid.GetLength(0) && guardCol >= 0 && guardCol < grid.GetLength(1))
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{
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// Move the guard following the rules
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MoveGuard(ref grid, ref guardRow, ref guardCol, ref guardDirection, ref possibleExtraLoops);
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// ArraySearching.Print2DCharArray(grid);
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// Console.WriteLine();
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// Console.WriteLine($"{guardRow},{guardCol} {guardDirection}");
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// tempCounter++;
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// if (tempCounter > 100)
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// {
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// break;
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// }
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}
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}
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private void SetGuardDirection(ref int moveX, ref int moveY, char guardDirection)
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{
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switch (guardDirection)
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{
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case '^':
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moveY = -1;
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break;
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case '>':
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moveX = 1;
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break;
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case 'v':
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moveY = 1;
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break;
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case '<':
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moveX = -1;
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break;
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default:
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throw new Exception("Invalid guard direction");
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break;
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}
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}
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private void MoveGuard(ref char[,] grid, ref int guardRow, ref int guardCol, ref char guardDirection,
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ref List<string> possibleExtraLoops)
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{
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// If there is something directly in front of you, turn right 90 degrees.
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// Otherwise, take a step forward.
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int moveX = 0;
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int moveY = 0;
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SetGuardDirection(ref moveX, ref moveY, guardDirection);
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try
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{
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// Check if there is something (#) directly in front of the guard
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char nextCell = grid[guardRow + moveY, guardCol + moveX];
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if (nextCell == '#')
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{
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// Turn right 90 degrees
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guardDirection = guardDirection switch
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{
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'^' => '>',
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'>' => 'v',
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'v' => '<',
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'<' => '^',
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_ => throw new Exception("Invalid guard direction")
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};
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}
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else
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{
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// Move forward
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guardRow += moveY;
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guardCol += moveX;
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// Mark the cell as visited
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grid[guardRow, guardCol] = 'X';
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}
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// Now check to see if the next cell could be a new obstruction
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// The guard will end up in a loop if it visits the same cell twice and is facing the same direction due to a new hazard
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// If the guard is on a path towards a hazard and there is another previously visited hazard to one side then a new hazard could be placed to
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// force the guard to loop back to the previously visited hazard
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int potentialMoveX = 0;
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int potentialMoveY = 0;
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SetGuardDirection(ref potentialMoveX, ref potentialMoveY, guardDirection);
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int searchArea = potentialMoveX == 0 ? grid.GetLength(0) - guardRow : grid.GetLength(1) - guardCol;
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// Check if there is something (#) directly in front of the guard in the new direction with a previously visited cell in front of it
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for (int i = 0; i < searchArea; i++)
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{
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if (potentialMoveX == 0)
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{
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// We are moving up or down
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if (grid[guardRow + potentialMoveY, guardCol] == '#')
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{
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// We have found a hazard
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// Check if there is a previously visited cell before it
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int potentialMoveYPreviousCell = potentialMoveY > 0 ? guardRow + 1 : guardRow - 1;
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if (grid[potentialMoveYPreviousCell, guardCol] == 'X')
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{
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// Mark the cell as a potential loop
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Console.WriteLine($"Potential loop at {guardCol + moveX},{guardRow + moveY}");
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// Add to possibleExtraLoops unless it is already there
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string loop = $"{guardCol + moveX},{guardRow + moveY}";
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if (!possibleExtraLoops.Contains(loop))
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{
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possibleExtraLoops.Add(loop);
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}
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}
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}
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}
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else
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{
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// We are moving sideways
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if (grid[guardRow, guardCol + potentialMoveX] == '#')
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{
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// We have found a hazard
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// Check if there is a previously visited cell before it
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int potentialMoveXPreviousCell = potentialMoveX > 0 ? guardCol - 1 : guardCol + 1;
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if (grid[guardRow, potentialMoveXPreviousCell] == 'X')
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{
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// We have found a potential loop
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Console.WriteLine($"Potential loop at {guardCol + moveX},{guardRow + moveY}");
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// Add to possibleExtraLoops unless it is already there
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string loop = $"{guardCol + moveX},{guardRow + moveY}";
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if (!possibleExtraLoops.Contains(loop))
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{
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possibleExtraLoops.Add(loop);
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}
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}
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}
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}
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}
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}
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catch (IndexOutOfRangeException ex)
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{
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// Move the guard out of the grid
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guardRow += moveY;
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guardCol += moveX;
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}
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catch (Exception ex)
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{
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Console.WriteLine(ex);
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throw;
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}
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}
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[TestCase(@"....#.....
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.........#
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..........
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..#.......
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.......#..
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..........
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.#..^.....
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........#.
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#.........
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......#...", 41)]
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[TestCase(null, 4711)] // The actual answer
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public void Part1(string? input, int? expected)
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{
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string[] lines = input != null ? input.Split("\n") : realData;
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char[,] grid = ArraySearching.ConvertListTo2DArray([.. lines]);
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List<string> possibleExtraLoops = new();
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TraverseGridAsGuard(ref grid, ref possibleExtraLoops);
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// Count how many cells the guard visited
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int result = 0;
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for (int r = 0; r < grid.GetLength(0); r++)
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{
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for (int c = 0; c < grid.GetLength(1); c++)
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{
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if (grid[r, c] == 'X')
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{
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result++;
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}
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}
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}
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if (expected != null)
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{
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Assert.That(result, Is.EqualTo(expected.Value));
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}
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Console.WriteLine($"Part 1: {result}");
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}
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[TestCase(@"....#.....
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.........#
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..........
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..#.......
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.......#..
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..........
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.#..^.....
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........#.
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#.........
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......#...", 6)]
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[TestCase(null, 1783)] // The actual answer
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public void Part2(string? input, int? expected)
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{
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string[] lines = input != null ? input.Split("\n") : realData;
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char[,] grid = ArraySearching.ConvertListTo2DArray([.. lines]);
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List<string> possibleExtraLoops = new();
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TraverseGridAsGuard(ref grid, ref possibleExtraLoops);
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if (expected != null)
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{
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Assert.That(possibleExtraLoops.Count, Is.EqualTo(expected.Value));
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}
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Console.WriteLine($"Part 2: {possibleExtraLoops.Count}");
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}
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}
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