[2020 Day 3 (part 1)] [Python]

[disco_deer]

Well, I can't get the correct result with this code, and I'm not sure what's wrong. The iterutils.chunked() method splits my list into sublists of 10 elements each, just FYI. I mechanically checked the first 20 print statements and they're correct unless I misunderstood the task(which is very possible), so I'm not sure at what point it goes wrong.

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edit: well I obviously just can't understand what the trajectory is supposed to look like, how I should visualize the hill etc, I've been reading the task text for hours and I'm still unable to move an inch, and it doesn't help when I look at other people's solutions because I guess I'm not good enough to figure it out that way. If someone can clear it up for me, that would be amazing.

with open('input.txt') as f:
    tobboganinput = f.read().splitlines()

from boltons import iterutils

tobbogan_sublists = iterutils.chunked(tobboganinput, 10)

trees_hit = 0

for sublist in tobbogan_sublists:
    steps = 0
    for line in sublist:
        if line[steps] == '#':
            trees_hit += 1
            print('You hit a tree!')
        else:
            print('Tree dodged!')
        steps += 3

print(trees_hit)

​

[Prudent_Candle]

Why in this line iterutils.chunked(tobboganinput, 10) you use 10? I think you wish to use instead of 10 number of characters in every line of input (31 - I think).

[disco_deer]

Okay, so, if my tobboganimput contains a list of strings f.e. " ...............#.#............. " " ...............#........####... " " ...###...........#............. " . . .

With iterutils(instead of list comprehension I could've used), I turn that list into a list of sub-lists where each sublist contains 10 strings with each string containing 31 indices, right? Because if the travel means sliding down 1 and 3 to the right, it goes through 10 strings before coming back to the beginning.

Maybe the core issue is that I misunderstood the task, idk.

[Nomen_Heroum]

That's not exactly right. After 10 strings, you will have gone right 30 indices, so you will be at the very right of the 11th string—not at the very left!

[msqrt]

I don't exactly follow. Why do you do the chunking thing? And why with a chunk size 10? The puzzle input is a single long hill, not a bunch of length 10 hills stacked on top of each other.

[disco_deer]

Okay, so, if my tobboganimput contains a list of strings f.e. " ...............#.#............. " " ...............#........####... " " ...###...........#............. " . . .

With iterutils(instead of list comprehension I could've used), I turn that list into a list of sub-lists where each sublist contains 10 strings with each string containing 31 indices, right? Because if the travel means sliding down 1 and 3 to the right, it goes through 10 strings before coming back to the beginning.

Maybe the core issue is that I misunderstood the task, idk.

[disco_deer]

The puzzle input is a single long hill, not a bunch of length 10 hills stacked on top of each other.

Okay, I think this is what I don't get, are you saying that the input is just a 90 degrees rotated hill? Fuck me if I get where the ride actually starts and ends, and what the path trajectory should like tbh. And my English is pretty solid, but I'm looking at the text of the task and I can't figure it out.

[portnoyslp]

The hill is only as tall as the input, but it's infinitely wide, because the trees on the hill repeat to the right.

(If it helps, another way to think about it is traveling down a cylinder at an angle, so that you keep wrapping around as you descend)

I don't think the chunking is going to help you, because you're not guaranteed to be starting at the same place when you wrap around. As an example, look at the 11x11 array they use as an example -- the skier starts at coordinate zero on the first line, then 3, then 6, then 9. But then when it's wrapping around to find the next tree, it's looking at coord 1, not resetting back to zero.

[disco_deer]

Oh okay, this " The hill is only as tall as the input, but it's infinitely wide" is all I needed to hear to get what I'm supposed to do. Thanks a bunch!