Add part 2

Day6/Program.cs

@@ -25,25 +25,83 @@ for (var j = 0; j < charArray.GetLength(1); j++)
     charArray[i, j] = lines[i][j];
 }
 
-var nextPosition = CalculateNextPosition(guardCurrentPosition.Item1, guardCurrentPosition.Item2, guardDirection);
+var part1 = Part1(guardCurrentPosition, guardDirection, charArray, visitedPositions);
+var part2 = Part2(guardCurrentPosition, charArray);
+Console.WriteLine($"Part1: {part1}\nPart2: {part2}");
 
-while (IsValid(nextPosition.Item1, nextPosition.Item2, charArray))
+int Part2((int,int) currentPosition, char[,] input)
 {
-    if (IsBlocked(nextPosition.Item1, nextPosition.Item2, charArray))
-    {
-        guardDirection = (Direction)(((int)guardDirection + 1) % 4);
-    }
-    else
-    {
-        guardCurrentPosition = (nextPosition.Item1, nextPosition.Item2);
-        visitedPositions.Add([guardCurrentPosition.Item1, guardCurrentPosition.Item2]);
-    }
+    var potentialLoopPositions = new List<(int row, int col)>();
 
-    nextPosition = CalculateNextPosition(guardCurrentPosition.Item1, guardCurrentPosition.Item2, guardDirection);
+    for (var i = 0; i < input.GetLength(0); i++)
+    for (var j = 0; j < input.GetLength(1); j++)
+    {
+        if ((i, j) == currentPosition || input[i, j] == '#') continue;
+        
+        var modifiedGrid = (char[,])input.Clone();
+        modifiedGrid[i, j] = '#';
+        
+        if (CausesLoop(currentPosition, modifiedGrid))
+        {
+            potentialLoopPositions.Add((i, j));
+        }
+    }
+    
+    return potentialLoopPositions.Count;
 }
 
-Console.WriteLine($"Part1: {visitedPositions.Select(x => $"r{x[0]},c{x[1]}").Distinct().Count()}");
-PrintMap(charArray, visitedPositions);
+bool CausesLoop((int row, int col) startPosition, char[,] input)
+{
+    var currentPosition = startPosition;
+    var currentDirection = Direction.Up;
+
+    var visited = new HashSet<((int row, int col), Direction)>();
+    visited.Add((currentPosition, currentDirection));
+
+    while (true)
+    {
+        var nextPosition = CalculateNextPosition(currentPosition.row, currentPosition.col, currentDirection);
+
+        if (!IsValid(nextPosition.Item1, nextPosition.Item2, input))
+            return false;
+
+        if (input[nextPosition.Item1, nextPosition.Item2] == '#')
+        {
+            currentDirection = (Direction)(((int)currentDirection + 1) % 4);
+        }
+        else
+        {
+            currentPosition = nextPosition;
+        }
+        
+        if (!visited.Add((currentPosition, currentDirection)))
+        {
+            return true;
+        }
+    }
+}
+
+int Part1((int,int) currentPosition, Direction direction, char[,] input, List<int[]> traveledPositions)
+{
+    var nextPosition = CalculateNextPosition(currentPosition.Item1, currentPosition.Item2, direction);
+
+    while (IsValid(nextPosition.Item1, nextPosition.Item2, input))
+    {
+        if (IsBlocked(nextPosition.Item1, nextPosition.Item2, input))
+        {
+            direction = (Direction)(((int)direction + 1) % 4);
+        }
+        else
+        {
+            currentPosition = (nextPosition.Item1, nextPosition.Item2);
+            traveledPositions.Add([currentPosition.Item1, currentPosition.Item2]);
+        }
+
+        nextPosition = CalculateNextPosition(currentPosition.Item1, currentPosition.Item2, direction);
+    }
+
+    return traveledPositions.Select(x => $"r{x[0]},c{x[1]}").Distinct().Count();
+}
 
 (int, int) CalculateNextPosition(int row, int col, Direction direction)
 {
@@ -55,26 +113,6 @@ bool IsValid(int row, int column, char[,] grid) => row >= 0 && row < grid.GetLen
 
 bool IsBlocked(int row, int col, char[,] grid) => grid[row, col] == '#';
 
-void PrintMap(char[,] input, List<int[]> visitedPositions)
-{
-    for (var i = 0; i < input.GetLength(0); i++)
-    {
-        for (var j = 0; j < input.GetLength(1); j++)
-        {
-            if (visitedPositions.Any(x => x[0] == i && x[1] == j) && input[i, j] != '^')
-            {
-                Console.Write("X");
-            }
-            else
-            {
-                Console.Write(input[i, j]);
-            }
-        }
-
-        Console.WriteLine();
-    }
-}
-
 enum Direction
 {
     Up,