Day 11. Seating System
Problem statement
https://adventofcode.com/2020/day/11 (mirror)My solution
Conway’s Game of Life was a recurring topic during AoC 2020, first encountered on day 11.
There is nothing fancy or smart in my solution. We save the input data to a 2D char matrix, so that modifying singular characters is more convenient.
The rest is just a straight and naive implementation of the problem requirements. We iterate over whole 2D matrix with a double for loop, count occupied neighbours of every seat in a third for loop (hidden from sight by CountOccupiedNeighbours method), change the occupation status for the next cycle if conditions are met, and remember if at least one flip occurred.
It’s not very fast (it’s barely acceptable), but it works.
A possible optimization would be precomputing the seat positions (as opposed to empty spaces .), and then precomputing the list of neighbours for each seat. If the input matrix was sparse, i.e. it inlcuded a high percentage of empty spaces, precomputing would make a dramatic difference. My input was dense, though, so I decided to skip it.