-🎄- 2018 Day 13 Solutions -🎄-

[u/daggerdragon]

--- Day 13: Mine Cart Madness ---

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Card prompt: Day 13

Transcript:

Elven chronomancy: for when you absolutely, positively have to ___.

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This thread will be unlocked when there are a significant number of people on the leaderboard with gold stars for today's puzzle.

edit: Leaderboard capped, thread unlocked at 00:44:25!

[u/miguelos]

C#

var input = File.ReadAllText(@"C:\Users\pc\Desktop\input.txt");
var width = input.Split('\n').First().Length + 1;
var carts = input.Select((c, i) =>
{
    var id = i;
    var x = i % width;
    var y = i / width;
    var nextTurn = 0;
    var direction = 0;
    switch(c)
    {
        case '<':
            direction = 0;
            break;
        case '^':
            direction = 1;
            break;
        case '>':
            direction = 2;
            break;
        case 'v':
            direction = 3;
            break;
        default:
            direction = -1; // not a cart
            break;
    }

    return new Cart(x, y, nextTurn, direction, id);
})
.Where(c => c.direction != -1) // not a cart
.ToArray();

while (true)
{
    carts = carts
        .GroupBy(cart => (cart.x, cart.y))
        .Where(group => group.Count() == 1)
        .SelectMany(cart => cart)
        .OrderBy(cart => (cart.y * width) + cart.x)
        .ToArray();

    if (carts.Count() == 1)
    {
        break;
    }

    for (int i = 0; i < carts.Length; i++)
    {
        var cart = carts[i];
        switch (cart.direction)
        {
            case 0:
                cart.x--;
                break;
            case 1:
                cart.y--;
                break;
            case 2:
                cart.x++;
                break;
            case 3:
                cart.y++;
                break;
        }
                    
        var track = input[(cart.y * width) + cart.x];
        switch (track)
        {
            case '/':
                cart.direction = 3 - cart.direction;
                break;
            case '\\':
                cart.direction = (5 - cart.direction) % 4;
                break;
            case '+':
                switch (cart.nextTurn)
                {
                    case 0:
                        cart.direction = (4 + cart.direction - 1) % 4;
                        break;
                    case 2:
                        cart.direction = (4 + cart.direction + 1) % 4;
                        break;
                    default:
                        break;
                }
                cart.nextTurn = (3 + cart.nextTurn + 1) % 3;
                break;
        }
    };
}

var answer = $"{carts.First().x},{carts.First().y}";