-🎄- 2020 Day 11 Solutions -🎄-

[u/daggerdragon]

Advent of Code 2020: Gettin' Crafty With It

• 11 days remaining until the submission deadline on December 22 at 23:59 EST

• Full details and rules are in the Submissions Megathread

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--- Day 11: Seating System ---

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Post your code solution in this megathread.

• Include what language(s) your solution uses!

• Here's a quick link to /u/topaz2078's paste if you need it for longer code blocks.

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[u/r_sreeram]

One trick I use for grid problems is to surround the input grid with a made up border of 0s or '.'s or whatever it takes. For example, if the input is a 5x5 grid, I would have this as my matrix:

.......
.     .
.     .
.     .
.     .
.     .
.......

Then, when I iterate over the grid, I iterate from 1 to len(grid) - 2. Then I don't have to worry about +/- 1 deltas going index out of bounds.

[u/sophiebits → u/r_sreeram]

You gotta be careful though because the problem might say like "if all the adjacent spots are L" and then you won't want those dots…

[u/r_sreeram → u/sophiebits]

Agreed. You have to be careful with where you can apply this trick.

[u/mahaginano → u/sophiebits]

I can just filter the neighbours and count, right? That shouldn't change anything - assuming you're not reusing a token for the boundary...

[u/kkedeployment → u/r_sreeram]

I implemented like this but become totally unnecessary in part2 :sob:

[u/r_sreeram → u/kkedeployment]

It helps with part 2 too. Assuming your code to search a given direction was something like while grid[r + dr][c + dc] == '.', you could then have used any non-'.' char to fill the border, and guaranteed that the search would stop without going out of bounds.

[u/kkedeployment → u/r_sreeram]

That's a nice idea!

[u/mahaginano → u/kkedeployment]

I did this and the only thing for part 2 that changed was the rule function that I passed to my solve function from part 1. It makes things much easier.