Advent of Code 2020 - Day 3

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.

A quick and easy one. This exercise consists on traversing a field defined by the input file following a given pattern, and counting how many of the positions traversed contain a '#' character (a tree in the puzzle). The pattern is given by a pair (r, c), meaning that each step advances r rows and c columns, with columns wrapping over if the width is exceeded.

Part 1

We are given a pattern, and we have to count the trees. Parsing the input is trivial and doesn't merit additional explanation.

The traversal itself is not especially complex, either. We update row and column with each step, using modulo arithmetic to easily wrap the columns around, and check if the new position is a tree. We end once we run out of rows.

Part 2

Rinse and repeat, with several patterns. If you were careful to use the condition row < height rather than row != height when checking the stopping condition everything will work, otherwise, some patterns may skip the row where row == height and never end.