Advent of Code 2023 - Day 14

var input = File.ReadAllLines("input.txt").Select(s => s.ToCharArray()).ToArray();

TiltNorth();

var part1 = 0;

for (var score = input.Length; score > 0; score--)
{
    part1 += input[^score].Count(c => c == 'O') * score;
}

Console.WriteLine($"Part 1: {part1}");

var cache = new Dictionary<string, int>();
var cycle = 1;

while (cycle <= 1_000_000_000)
{
    TiltNorth();
    TiltWest();
    TiltSouth();
    TiltEast();

    var current = string.Join(string.Empty, input.SelectMany(c => c));

    if (cache.TryGetValue(current, out var cached))
    {
        var remaining = 1_000_000_000 - cycle - 1;
        var loop = cycle - cached;

        var loopRemaining = remaining % loop;
        cycle = 1_000_000_000 - loopRemaining - 1;
    }

    cache[current] = cycle++;
}

var part2 = 0;

for (var score = input.Length; score > 0; score--)
{
    part2 += input[^score].Count(c => c == 'O') * score;
}

Console.WriteLine($"Part 2: {part2}");
return;

void TiltNorth()
{
    for (var row = 1; row < input.Length; row++)
    {
        for (var col = 0; col < input[row].Length; col++)
        {
            var c = input[row][col];

            if (c != 'O')
            {
                continue;
            }

            var previous = 1;
            while (input[row - previous][col] == '.')
            {
                input[row - previous][col] = 'O';
                input[row - previous + 1][col] = '.';
                previous++;

                if (row - previous < 0)
                {
                    break;
                }
            }
        }
    }
}

void TiltSouth()
{
    for (var row = input.Length - 2; row >= 0; row--)
    {
        for (var col = 0; col < input[row].Length; col++)
        {
            var c = input[row][col];

            if (c != 'O')
            {
                continue;
            }

            var previous = 1;
            while (input[row + previous][col] == '.')
            {
                input[row + previous][col] = 'O';
                input[row + previous - 1][col] = '.';
                previous++;

                if (row + previous >= input.Length)
                {
                    break;
                }
            }
        }
    }
}

void TiltWest()
{
    for (var row = 0; row < input.Length; row++)
    {
        for (var col = 1; col < input[row].Length; col++)
        {
            var c = input[row][col];

            if (c != 'O')
            {
                continue;
            }

            var previous = 1;
            while (input[row][col - previous] == '.')
            {
                input[row][col - previous] = 'O';
                input[row][col - previous + 1] = '.';
                previous++;

                if (col - previous < 0)
                {
                    break;
                }
            }
        }
    }
}

void TiltEast()
{
    for (var row = 0; row < input.Length; row++)
    {
        for (var col = input[row].Length - 2; col >= 0; col--)
        {
            var c = input[row][col];

            if (c != 'O')
            {
                continue;
            }

            var previous = 1;
            while (input[row][col + previous] == '.')
            {
                input[row][col + previous] = 'O';
                input[row][col + previous - 1] = '.';
                previous++;

                if (col + previous >= input[row].Length)
                {
                    break;
                }
            }
        }
    }
}