Advent of Code 2020 - Day 21

This is a running series of posts on the Advent of Code 2020. The introductory post has the details, including the accompanying GitHub repo, in case you reached this directly.

In this problem we get some foods (as the list of ingredients) and allergens contained (although some maybe omitted). We will read the input as a list of tuples, one tuple for each food containing the set of ingredients and the set of allergens.

Part 1

This part requires finding out the ingredients that do not contain any allergens. We will do it in two steps.

First, we will find the candidate ingredients for each allergen. We just go over each food, and add its ingredients to the set of candidates for each allergen it contains. The answer is the set of ingredients not in the union of the candidates to all allergens.

Part 2

We now need to identify the sources of each allergen. We will start from the candidates determined in part 1, and apply the same elimination strategy we applied for identifying fields in a previous problem.