Advent of Code 2020 (Rust)

To study the Rust programming language, and improve my Vimming meanwhile, I am attempting last year’s Advent of Code.

Day 1

Part 1

The challenge is to find two elements of a data set that sum to 2020. I solved this problem recursively. The data passes into a function that compares the first element to every other element of the set. Then it passes a slice of its input, which excludes the first element, into itself. When two compared elements sum to 2020, it returns a tuple of those elements. If the size of the input is less than 2, it returns an error.

Part 2

The challenge of Part 2 is to make my previous solution scale. It is only required to evaluate three items, but I felt it was in the spirit of this challenge to write a solution that has arbitrary parameters. My new recursive function now nests itself n times deep to find n elements that sum to 2020. n is 3 in this example.

Day 2

Part 1

The challenge is to sum the count of elements in a list that fulfill certain parameters. I solved this problem procedurally. A mutable count of valid elements is initialized, and I then iterate through every element of the data set. The elements are human readable text, so I split each element by =’ ‘= and =’-‘= characters, then parse the substrings into the data that I need. I branchlessly increment the counting variable with a boolean condition that casted to an unsigned integer.

Part 2

This challenge is similar to Part 1, but it requires a different condition to evaluate. I simply hard coded a different condition, but in retrospect, I believe that passing a closure into a function to sum the count of valid elements would have been better in the spirit of this challenge.

Day 3

Part 1

The challenge is to traverse a grid with a finite Y dimension and an infinite X dimension (with elements that tile). I wrote a recursive function to traverse this grid in increments of slope 3/1, exiting when its y position exceeds the height of the grid. It branchlessly increments a counter variable when the element at its position is =’#’=, and returns this count.

Part 2

This challenge requires an arbitrary slope. I represented slopes as tuples of two integral elements, and initialized an array of 5 slopes. I learned to use some of Rust’s functional features I have read about, and mapped this array to their counts with a closure of the previous recursive function. That map is collected into a vector of unsigned integers, which is piped into a product function.