AdventOfCode/2024/Day04CSharp/Program.cs

var exParsed = new Day04Parsed("example-input.txt");

Console.WriteLine("Example Part01: {0}", exParsed.GetPart01());
Console.WriteLine("Example Part02: {0}", exParsed.GetPart02());

var pzParsed = new Day04Parsed("puzzle-input.txt");

Console.WriteLine("Puzzle Part01: {0}", pzParsed.GetPart01());
Console.WriteLine("Puzzle Part02: {0}", pzParsed.GetPart02());

class Day04Parsed : AdventCommon.ParsedInput
{
    static readonly string WORD_TO_SEARCH = "XMAS";

    List<string> letterGrid = new List<string>();

    public Day04Parsed(string fileName) : base(fileName)
    {
    }

    public override int GetPart01()
    {
        int count = 0;

        for (int i = 0; i < letterGrid.Count; i++)
        {
            var row = GetRow(i);

            for (int j = 0; j < row.Length; j++)
            {
                var words = GetWords(i, j);
                count += CountWords(words, WORD_TO_SEARCH);
            }
        }

        return count;
    }

    public override int GetPart02()
    {
        int count = 0;

        for (int i = 0; i < letterGrid.Count; i++)
        {
            var row = GetRow(i);
            for (int j = 0; j < row.Length; j++)
            {
                if (IsMASX(i, j)) { count++; }
            }
        }

        return count;
    }

    public bool IsMASX(int i, int j)
    {
        try
        {
            string wordToSearch = "MAS";
            string rwordToSearch = new string(wordToSearch.Reverse().ToArray());

            if (GetEntry(i,j) != 'A') { return false; }

            string backwardSlash = String.Format("{0}{1}{2}", GetEntry(i-1,j-1), GetEntry(i,j), GetEntry(i+1,j+1));
            string forwardSlash = String.Format("{0}{1}{2}", GetEntry(i-1,j+1), GetEntry(i,j), GetEntry(i+1,j-1));

            if (    (String.Compare(backwardSlash, wordToSearch) == 0 || String.Compare(backwardSlash, rwordToSearch) == 0)
                &&  (String.Compare(forwardSlash, wordToSearch) == 0 || String.Compare(forwardSlash, rwordToSearch) == 0))
            {
                return true;
            }
        } 
        catch (Exception) { }

        return false;
    }

    string GetRow(int i) => letterGrid[i];
    string GetColumn(int i) {
        string toRet = "";
        foreach (var line in letterGrid)
        {
            toRet += line[i];
        }
        return toRet;
    }

    char GetEntry(int i, int j) => letterGrid[i][j];

    static int CountWords(List<string> words, string wordToSearch)
    {
        int count = 0;

        string rwordToSearch = new string(wordToSearch.Reverse().ToArray());

        foreach (var word in words)
        {
            if (String.Compare(word, wordToSearch) == 0 || String.Compare(word, rwordToSearch) == 0)
            {
                count++;
            }
        }

        return count;
    }

    List<string> GetWords(int i, int j)
    {
        List<string> words = new List<string>();

        // Scan only with X
        if (GetEntry(i, j) != 'X')
        {
            return words;
        }

        var row = GetRow(i);
        var col = GetColumn(j);

        // Get horizontal
        try
        {
            words.Add(row.Substring(j, WORD_TO_SEARCH.Length));
        } catch (Exception) { }

        // Get backwards
        try
        {
            words.Add(row.Substring(j-(WORD_TO_SEARCH.Length-1), WORD_TO_SEARCH.Length));
        } catch (Exception) { }

        // Get vertical down
        try
        {
            words.Add(col.Substring(i, WORD_TO_SEARCH.Length));
        } catch (Exception) { }

        // Get vertical "up"
        try
        {
            words.Add(col.Substring(i-(WORD_TO_SEARCH.Length-1), WORD_TO_SEARCH.Length));
        } catch (Exception) { }

        // Top Right Diag
        try
        {
            string diag = "";
            for (int x = i, y = j; y < j+WORD_TO_SEARCH.Length; x--, y++)
            {
                diag += GetEntry(x, y);
            }
            words.Add(diag);
        } catch (Exception) { }

        // Down right Diag
        try
        {
            string diag = "";
            for (int x = i, y = j; y < j + WORD_TO_SEARCH.Length; x++, y++)
            {
                diag += GetEntry(x, y);
            }
            words.Add(diag);
        } catch (Exception) { }

        // Down left Diag
        try
        {
            string diag = "";
            for (int x = i, y = j; y > j - WORD_TO_SEARCH.Length; x++, y--)
            {
                diag += GetEntry(x, y);
            }
            words.Add(diag);
        } catch (Exception) { }

        // Up right Diag
        try
        {
            string diag = "";
            for (int x = i, y = j; y > j - WORD_TO_SEARCH.Length; x--, y--)
            {
                diag += GetEntry(x, y);
            }
            words.Add(diag);
        }
        catch (Exception) { }

        return words;
    }

    public override bool ParseLine(string line, object? context = null)
    {
        letterGrid.Add(line);
        return true;
    }
}