This is a thread to discuss Day9
https://adventofcode.com/2021/day/9
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You have a speedy computer, when i run your code: part 1 = 500ms, part 2 = 2300ms
It was brand new last week
only part 1 for me :
....1st attempt: 6.6 sec
....2nd attempt: 2.1 sec
....3rd attempt: 1.2 sec
My 1st idea was like you: a border of 9.
But i try to without this border: bad idea. The code as much "if then else" than i have teeths in my mouth (I have a lot of teeths).
I think adding the border is the key to simplifying this one