public string SolvePart2(string input, IProgress <string> progress = null)
{
Parse(input);
while (true)
{
if (Carts.Count(c => !c.Crashed) == 1)
{
var cart = Carts.First(c => !c.Crashed);
return((cart.X, cart.Y).ToString());
}
foreach (var cart in Carts.OrderBy(c => c.Y).ThenBy(c => c.X))
{
if (cart.Crashed)
{
continue;
}
var next = cart.GetNextLocation();
var otherCart = Carts.FirstOrDefault(c => !c.Crashed && c.X == next.x && c.Y == next.y);
if (otherCart != null)
{
cart.Crashed = true;
otherCart.Crashed = true;
}
char track = LookAhead(cart);
switch (cart.Direction)
{
case Direction.Up:
cart.Y--;
switch (track)
{
case '\\':
cart.Direction = Direction.Left;
break;
case '/':
cart.Direction = Direction.Right;
break;
case '+':
IntersectionTurn(cart);
break;
}
break;
case Direction.Down:
cart.Y++;
switch (track)
{
case '\\':
cart.Direction = Direction.Right;
break;
case '/':
cart.Direction = Direction.Left;
break;
case '+':
IntersectionTurn(cart);
break;
}
break;
case Direction.Left:
cart.X--;
switch (track)
{
case '\\':
cart.Direction = Direction.Up;
break;
case '/':
cart.Direction = Direction.Down;
break;
case '+':
IntersectionTurn(cart);
break;
}
break;
case Direction.Right:
cart.X++;
switch (track)
{
case '\\':
cart.Direction = Direction.Down;
break;
case '/':
cart.Direction = Direction.Up;
break;
case '+':
IntersectionTurn(cart);
break;
}
break;
default:
throw new ArgumentOutOfRangeException();
}
}
}
}
