R/day2.R

In moodymudskipper/adventofcode2021: My Solutions for Advent Of Code 2021

#' day 2
#'
#' @export
day2 <- function() {
  # data
  file <- system.file("extdata/day2.txt", package = "adventofcode2021")
  input <- scan(file, what = character(), sep = "\n", quiet = TRUE)

  # part 1
  # transform code into complex arithmetic and eval
  code <- paste(input, collapse = "")
  code <- gsub("forward ", "+", code)
  code <- gsub("down (\\d+)", "+\\1i", code)
  code <- gsub("up (\\d+)", "-\\1i", code)
  pos <- eval(str2lang(code))
  part1 <- Re(pos) * Im(pos)

  # part1 again
  # same with vectors rather than complex values
  code <- paste(input, collapse = "")
  code <- gsub("forward (\\d+)", "+c(\\1,0)", code)
  code <- gsub("down (\\d+)", "+c(0,\\1)", code)
  code <- gsub("up (\\d+)", "-c(0,\\1)", code)
  pos <- eval(str2lang(code))
  part1 <- prod(pos)

  # part 2
  # convert instructions to functions and reduce
  code <- gsub("forward (\\d+)", "\\\\(x) x + c(\\1, x[3] * \\1, 0)", input)
  code <- gsub("down (\\d+)", "\\\\(x) x + c(0, 0, \\1)", code)
  code <- gsub("up (\\d+)", "\\\\(x) x - c(0, 0, \\1)", code)
  pos <- Reduce(function(x, f) f(x), lapply(code, \(f) eval(str2lang(f))), c(0,0,0))
  part2 <- prod(pos[1:2])

  list(part1 = part1, part2 = part2)
}