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https://github.com/tjmahr/adventofcode21
My solutions (R) for Advent of Code 2021
https://github.com/tjmahr/adventofcode21
advent-of-code advent-of-code-2021 r
Last synced: 24 days ago
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My solutions (R) for Advent of Code 2021
- Host: GitHub
- URL: https://github.com/tjmahr/adventofcode21
- Owner: tjmahr
- License: gpl-3.0
- Created: 2021-12-01T15:29:29.000Z (about 3 years ago)
- Default Branch: main
- Last Pushed: 2022-01-07T15:56:29.000Z (about 3 years ago)
- Last Synced: 2025-01-04T01:05:25.603Z (about 1 month ago)
- Topics: advent-of-code, advent-of-code-2021, r
- Language: R
- Homepage: http://adventofcode.com/2021
- Size: 636 KB
- Stars: 0
- Watchers: 3
- Forks: 0
- Open Issues: 0
-
Metadata Files:
- Readme: README.md
- License: LICENSE.md
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README
# adventofcode21
These are my solutions to [Advent of Code
2021](http://adventofcode.com/2021), a series of 25 programming puzzles.
## Installation
You can install adventofcode21 from [GitHub](https://github.com/) with:
``` r
# install.packages("devtools")
devtools::install_github("tjmahr/adventofcode21")
```
But you probably shouldn't do that.
## Package overview
The package infrastructure was automatically generated for each day using
[my aoc package](https://github.com/tjmahr/aoc) and its `use_day(day, year)`
function.
The `/R` folder contains the R functions I wrote for each day. I used
some light test-driven development for the puzzles. That is, each puzzle
description provides some example inputs and outputs. Before tackling
the main test input, I write a unit-test in `/tests` that confirms that
my solution can correctly reproduce the examples. The `/inst` directory
contains the code to handle the main test input for each day.
I limited the amount of package dependencies used for these puzzles to
maximize future compatibility and to make sure that it is mostly *my
code* that solves the problems. For example, if a puzzle requires
answering questions about the data in a tree-like structure, it would be
kind of cheating for me to find a library for building and traversing
trees to tackle the problem. It’s *advent of code*, not *advent of
load*.
I have allowed myself to use:
- base, stats, utils, tools, and so on: the base R packages
In the past I have allowed myself to use magrittr, rlang and stringr, but
the native pipe `|>` eliminates the need for magrittr and some grit
eliminates the need for the others.
I’ve put my R source code under a GPL-3 license. It should not apply to
the puzzle descriptions in the code comments at the top of each file. I
did not write those descriptions.
## Coding approaches
Here are the programming tasks and techniques I used for the various
puzzles.
- 00a/b *Write puzzle description like this:* Period separated strategies. Enumerated.
- 16a/b *Decode packets and run code inside of them:* Recursion (parsing). Creating and evaluating R code.
- 23a/b *Solve a tile sliding game:* No code. Solved by hand
(see inst/notes-day-22b-moves.R).
- 24a/b *Find inputs that produce 0 for a program:* Objects via closures.
Creating and evaluating R code. Static analysis.
- 25a/b *Simulate movement in a grid that wraps around:* Matrix subsetting.
Mod1.
Book-keeping: basic programming where I keep track of some
changing state like a position in a vector.
Math: Studying the problem and using math to find a shortcut
that lets me skip some computations.
Creating and evaluating R code: Constructing R function calls from the input and
evaluating them in R. Converting the problem into running an R script.
## Helpful builtin R functions
Here are some functions that have I discovered, rediscovered, or
otherwise appreciate somewhat more from these exercises:
### 2021 list
- [`which()`](https://rdrr.io/r/base/which.html) but with `arr.ind = TRUE` for easier matrix subsetting
- [`simplify2Array()`](https://rdrr.io/r/base/lapply.html) for combining a list of vectors into a matrix
- [`..1`, `..2`](https://rdrr.io/r/base/dots.html) for creating functions like `v_eq <- function(...) as.numeric(..1 == ..2)`
### 2020 list
- [`complete.cases()`](https://rdrr.io/r/stats/complete.cases.html)
- [`intersect()`](https://rdrr.io/r/base/sets.html)
- [`lengths()`](https://rdrr.io/r/base/lengths.html)
- [`modifyList()`](https://rdrr.io/r/utils/modifyList.html)
- [`outer()`](https://rdrr.io/r/base/outer.html)
- [`prod()`](https://rdrr.io/r/base/prod.html)
- [`strtoi()`](https://rdrr.io/r/base/strtoi.html)
- [`chartr()`](https://rdrr.io/r/base/chartr.html)
- [`Find() and Position()`](https://rdrr.io/r/base/funprog.html)