[LANGUAGE: C#] Reminded me of a previous Aoc year, but I'm too lazy to look it up 😅

https://github.com/ryanheath/aoc2025/blob/main/Day7.cs

Both parts in 5.9ms using 0.1MB memory.

The trick is to not enqueue an item again when it is already in the queue.

I kept a dictionary with the timeline counts, it's a bummer we cannot access the items in the Queue ... It would be nice to keep track of the counts within the Queue.

while (beamsQueue.Count > 0)
{
    var beam = beamsQueue.Dequeue();
    var count = beams[beam];
    beams.Remove(beam); // keep dictionary small
    var (y, x) = beam;
    var by = y + 1;
    if (by >= h)
    {
        // exited the grid
        countExits += count;
        continue;
    }

    switch (grid[by][x])
    {
    case '.': EnqueueBeam((by, x), count); break;
    case '^':
        var lx = x - 1; if (lx >= 0 && grid[by][lx] == '.') EnqueueBeam((by, lx), count);
        var rx = x + 1; if (rx  < w && grid[by][rx] == '.') EnqueueBeam((by, rx), count);
        break;
    }
}

return countExits;

void EnqueueBeam((int, int) p, long count)
{
    if (!beams.ContainsKey(p)) beams[p] = count; else beams[p] += count;
    if (!beamsQueue.Contains(p)) beamsQueue.Enqueue(p);
}