Module aoc::year2021::day13

Transparent Origami

There are 2 possible approaches to tracking the position of dots after each fold:

• A HashSet that will collapse duplicate entries
• An array of sufficient dimensions to track every possible coordinate.

We will use both approaches for speed, the first in part 1 and the second in part 2.

For part 2 we can determine the final size of the paper by taking the last x and y coordinates from the fold instructions. It’s then faster and more convenienent to process each point completely and update the final location, than to step through intermediate folds.

Structs

• Input

Enums

• Fold

Functions

• fold_horizontal 🔒
  Fold point at x coordinate, doing nothing if the point is to the left of the fold line.
• fold_vertical 🔒
  Fold point at y coordinate, doing nothing if the point is above the fold line.
• parse
  Parse the input into collections of Point and Fold structs.
• part1
  Fold once then count dots. The sample data folds along y and my input folded along x testing both possibilities.
• part2
  Decode secret message.