My day 17: <https://github.com/jorispz/aoc-2019/bl...

# advent-of-code

[Joris PZ]

My day 17: https://github.com/jorispz/aoc-2019/blob/master/src/commonMain/kotlin/day17/p17.kt

I went low-tech and did part 2 by hand using Excel, given the small world map it seemed a lot quicker than creating an algorithm

[marstran]

I also wonder if all possible paths will be reducable to 3 functions. I just found the first path using a depth-first search, and it happened to work.

[Kroppeb]

The generater probably starts with 3 functions and and a main and generates the map using that. Probably also a check preventing a path to go over itself (still allowing crossing)

[marstran]

Probably, but that will only ensure that at least 1 path can be written as 3 functions. But there are multiple other paths that may not have the same property (depending if you go left or right in an intersection for example).

[Kroppeb]

the following algo seems to always visit all points once, and intersections twice:

while(True){
    when{
        canMoveForwards() -> moveForwards()
        canMoveLeft() -> turnLeft()
        canMoveRight() -> turnRight()
        else -> break //finished
    }
}

[marstran]

It might reach a dead end though (assuming the “canMove” function is just checking if the next field is a scaffold).

[Kroppeb]

It won't

[marstran]

Why?

[Kroppeb]

Look at your scaffold

[marstran]

What if the first turn to the left ends up in a dead end?

[Kroppeb]

?

[marstran]

Let me create an example. 2 sec.

[marstran]

If the map looks like this, then you will reach the dead end before making the loop:

...........
.#########.
.#.......#.
.#..#....#.
.#########.
....#......
....#......
....###^...

[Kroppeb]

mmh

[Kroppeb]

Yeah i don't think it will do that

[marstran]

But then you’re assuming things about the input 😛 I was wondering if it would work in general.

[Kroppeb]

Yeah, but assuming things about the input is part of the game

[Kroppeb]

It's quite easy to make a checker for that

[marstran]

Sure, but it was not what I asked.

[Kroppeb]

I'm pretty sure the input is crafted in a way that makes the desired path quite obvious. aka don't turn if you don't have to

[marstran]

Would be more impressive if they managed to make every path reducible to 3 functions 😛

[marstran]

I actually checked now. I found a path by going right first, then left, then forward. It was not reducible.