Part 1
The problem requires us to determine how many rolls of paper (@) on a 2D grid are accessible to forklifts.
A roll is considered accessible if it has fewer than 4 neighboring paper rolls in its 8 adjacent directions
(horizontally, vertically, and diagonally).
To solve Part 1:
- We iterate over every cell in the grid.
- When we encounter a paper roll (
@), we count how many of its 8 surrounding neighbors also contain@. - If the neighbor count is strictly less than 4, we mark this roll as accessible.
- Finally, we return the total count of all accessible paper rolls.
Part 2
In Part 2, the process becomes iterative. Once accessible paper rolls are identified, the forklifts can remove them
(replacing them with empty space .). Removing paper rolls changes the surrounding neighborhood counts, potentially
making previously inaccessible rolls accessible in subsequent steps.
We simulate this removal process in a loop:
- In each iteration, we locate all currently accessible paper rolls (
@cells with fewer than 4@neighbors). - If no accessible rolls are found, the process terminates.
- Otherwise, we remove all found accessible rolls by mutating their positions in the grid to empty cells (
.), accumulate the number of removed rolls into a running total, and repeat. - Once no more rolls can be accessed, we return the total count of removed paper rolls across all iterations.