08: Two-Factor Authentication

library(mistlecode)

To install `mistlecode` yourself, run `devtools::install_github('guslipkin/mistlecode')`.

 Also loading:  cipheR data.table dplyr purrr slider stringr tidyverse glue

dt <- readLines("input.txt")

Part 1

A short ride on the struggle bus, but I actually really liked this one! And I found a better way to make cyclical vectors which is nice. I’ll probably add it to mistlecode…

m <- matrix(" ", nrow = 6, ncol = 50)

cycle <- function(x, n) {
  n <- n %% length(x)
  if (n == 0) x else c(tail(x, n), head(x, -n))
}

parse_input <- function(x) {
  y <-
    str_match(x, "(\\d+)(x| by )(\\d+)")[1, c(2, 4)] |>
    as.numeric()
  a <- y[1]; b <- y[2];
  if (str_detect(x, "rect")) {
    x <- \(m) { m[1:b, 1:a] <- "#"; m; }
  } else {
    a <- a + 1
    if (str_detect(x, "rotate row")) {
      x <- \(m) { m[a,] <- cycle(m[a,], b); m; }
    } else if (str_detect(x, "rotate col")) {
      x <- \(m) { m[,a] <- cycle(m[,a], b); m; }
    }
  }
  return(x)
}

f_dt <- map(dt, parse_input)
i <- seq_along(f_dt)
while (length(i) > 0) {
  m <- f_dt[[i[1]]](m)
  i <- i[-1]
}
sum(m == "#")

[1] 121

Part 2

Plotting for Advent is always fun! Just need to mess with the scaling a bit.

matrix_to_coords(m) |>
  data.frame() |>
  filter(data == "#") |>
  mutate(across(row:col, as.numeric)) |>
  ggplot() +
  geom_tile(aes(x = col, y = -row)) +
  theme_void() +
  ylim(-18, 0)