This is Day 13 of Advent of Code 2023! If you would like to solve the problems before looking at the solution, you can find them here.

In part 1 of Day 13, we have symmetries! We have been given a file with multiple matrices, each made up of dots and hashes, and each of them has a single line of symmetry associated with it. As a data cleaning exercise, I add hyphens between each character for my own ease of understanding. In order to find the axis of symmetry, I went through each line and listed out the potential axes of symmetry - if the intersection of all these lists contained a value, we have our answer, if not, the axis is between two rows, and we transpose the matrix and parse it again. As I write this post, I realize that I didn't check for the non-existence of a vertical axis before looking for a horizontal axis, but it was pretty fast regardless, so no harm done. Click here to jump to the part 2 discussion.

For part 2 of Day 13, we have smudge in the matrix, and we need to find out a new axis of symmetry by flipping one element in the matrix - the confusing part here was that the new axis of symmetry had to be different from the old axis of symmetry, took me a bit of debugging and rereading to figure that out. Outside of that, just the same as part 1 but took a few seconds takes instead of being instantaneous.

That's all folks! If you made it this far, enjoy some AI art generated by u/encse using the prompt for this puzzle.

Cheers,

Devang