Another Casual Coder

To solve this Advent of Code (parts 1 and 2), I used Breadth-First Search (BFS) to keep moving the guard as well as Finite State Machine (FSM) to control the directions. This solves part 1 easily. Part 2 can be solved using the same technique, takes a little longer since you need to try every empty cell, but it eventually does the trick (takes a min or so). Code is down below, cheers, ACC.

Day 6 - Advent of Code 2024

using System.IO;
using System.Collections;
using System;
using System.Text;
using System.Text.RegularExpressions;
using System.ComponentModel.DataAnnotations;
Process2();
void Process()
{
 string fileName = "input.txt";
 FileInfo fileInfo = new FileInfo(fileName);
 StreamReader sr = fileInfo.OpenText();
 List map = new List();
 int startRow = 0;
 int startCol = 0;
 while (!sr.EndOfStream)
 {
 string line = sr.ReadLine().Trim();
 map.Add(new StringBuilder(line));
 int indexStart = line.IndexOf('^');
 if (indexStart >= 0)
 {
 startRow = map.Count - 1;
 startCol = indexStart;
 }
 }
 sr.Close();
 int retVal = ProcessExitMap(map, startRow, startCol);
 Console.WriteLine(retVal);
}
void Process2()
{
 string fileName = "input.txt";
 FileInfo fileInfo = new FileInfo(fileName);
 StreamReader sr = fileInfo.OpenText();
 List map = new List();
 int startRow = 0;
 int startCol = 0;
 while (!sr.EndOfStream)
 {
 string line = sr.ReadLine().Trim();
 map.Add(new StringBuilder(line));
 int indexStart = line.IndexOf('^');
 if (indexStart >= 0)
 {
 startRow = map.Count - 1;
 startCol = indexStart;
 }
 }
 sr.Close();
 int retVal = 0;
 for (int row = 0; row < map.Count; row++)
 {
 for (int col = 0; col < map[row].Length; col++)
 {
 if (map[row][col] == '.')
 {
 map[row][col] = '#';
 if (ProcessExitMap(map, startRow, startCol) == -1)
 retVal++;
 map[row][col] = '.';
 }
 }
 }
 Console.WriteLine(retVal);
}
void PrintMap(List map, int guardRow, int guardCol)
{
 for (int row = 0; row < map.Count; row++)
 {
 for(int col = 0; col < map[row].Length;col++)
 {
 if (row == guardRow && col == guardCol)
 {
 Console.Write("@");
 }
 else
 {
 Console.Write(map[row][col]);
 }
 }
 Console.WriteLine();
 }
 Console.ReadLine();
}
int ProcessExitMap(List map, int startRow, int startCol)
{
 Queue
 queue = new Queue
();
 HashSet visited = new HashSet();
 MapCell initialCell = new MapCell(startRow, startCol, 1, "up");
 queue.Enqueue(initialCell);
 visited.Add(initialCell.key);
 HashSet distinctPositionsVisited = new HashSet ();
 while (queue.Count > 0)
 {
 MapCell currentCell = queue.Dequeue();
 //Console.WriteLine("DISTINCT POSITIONS: {0}", distinctPositionsVisited.Count);
 //PrintMap(map, currentCell.row, currentCell.col);
 if (currentCell.row < 0 ||
 currentCell.row >= map.Count ||
 currentCell.col < 0 ||
 currentCell.col >= map[startRow].Length)
 {
 //Console.WriteLine();
 //Console.WriteLine("FOUND: {0}", distinctPositionsVisited.Count);
 return distinctPositionsVisited.Count;
 }
 string position = currentCell.row.ToString() + "@" + currentCell.col.ToString();
 if(!distinctPositionsVisited.Contains(position))
 distinctPositionsVisited.Add(position);
 int newRow = 0;
 int newCol = 0;
 string newDirection = "";
 switch (currentCell.direction)
 {
 case "up":
 if (currentCell.row - 1 >= 0 && map[currentCell.row - 1][currentCell.col] == '#')
 {
 newRow = currentCell.row;
 newCol = currentCell.col;
 newDirection = "right";
 MapCell newCell = new MapCell(newRow, newCol, currentCell.numberSteps, newDirection);
 queue.Enqueue(newCell);
 }
 else
 {
 newRow = currentCell.row - 1;
 newCol = currentCell.col;
 newDirection = "up";
 MapCell newCell = new MapCell(newRow, newCol, currentCell.numberSteps + 1, newDirection);
 if (!visited.Contains(newCell.key))
 {
 queue.Enqueue(newCell);
 visited.Add(newCell.key);
 }
 }
 break;
 case "down":
 if (currentCell.row + 1 < map.Count && map[currentCell.row + 1][currentCell.col] == '#')
 {
 newRow = currentCell.row;
 newCol = currentCell.col;
 newDirection = "left";
 MapCell newCell = new MapCell(newRow, newCol, currentCell.numberSteps, newDirection);
 queue.Enqueue(newCell);
 }
 else
 {
 newRow = currentCell.row + 1;
 newCol = currentCell.col;
 newDirection = "down";
 MapCell newCell = new MapCell(newRow, newCol, currentCell.numberSteps + 1, newDirection);
 if (!visited.Contains(newCell.key))
 {
 queue.Enqueue(newCell);
 visited.Add(newCell.key);
 }
 }
 break;
 case "right":
 if (currentCell.col + 1 < map[currentCell.row].Length && map[currentCell.row][currentCell.col + 1] == '#')
 {
 newRow = currentCell.row;
 newCol = currentCell.col;
 newDirection = "down";
 MapCell newCell = new MapCell(newRow, newCol, currentCell.numberSteps, newDirection);
 queue.Enqueue(newCell);
 }
 else
 {
 newRow = currentCell.row;
 newCol = currentCell.col + 1;
 newDirection = "right";
 MapCell newCell = new MapCell(newRow, newCol, currentCell.numberSteps + 1, newDirection);
 if (!visited.Contains(newCell.key))
 {
 queue.Enqueue(newCell);
 visited.Add(newCell.key);
 }
 }
 break;
 case "left":
 if (currentCell.col - 1 >= 0 && map[currentCell.row][currentCell.col - 1] == '#')
 {
 newRow = currentCell.row;
 newCol = currentCell.col;
 newDirection = "up";
 MapCell newCell = new MapCell(newRow, newCol, currentCell.numberSteps, newDirection);
 queue.Enqueue(newCell);
 }
 else
 {
 newRow = currentCell.row;
 newCol = currentCell.col - 1;
 newDirection = "left";
 MapCell newCell = new MapCell(newRow, newCol, currentCell.numberSteps + 1, newDirection);
 if (!visited.Contains(newCell.key))
 {
 queue.Enqueue(newCell);
 visited.Add(newCell.key);
 }
 }
 break;
 }
 }
 return -1;
}
class MapCell
{
 public int row = 0;
 public int col = 0;
 public int numberSteps = 0;
 public string direction = "";
 public string key = "";
 public MapCell(int row, int col, int numberSteps, string direction)
 {
 this.row = row;
 this.col = col;
 this.numberSteps = numberSteps;
 this.direction = direction;
 this.key = row.ToString() + "@" + col.ToString() + "@" + direction.ToString();
 }
}