R/12-1.R

In soniamitchell/adventofcode: My Advent of Code solutions

#' Day 12: Passage Pathing
#' @source <https://adventofcode.com/2021/day/12>
#' @name day12
#'
NULL

#' @rdname day12
#' @param path file path
#' @export
#'
read_day12 <- function(path) {
  dat <- path |>
    read.table(sep = "-")
  rbind(dat, dplyr::rename(dat, V1 = V2, V2 = V1)) |>
    dplyr::rename(from = V1,
                  to = V2) |>
    dplyr::filter(from != "end",
                  to != "start")
}

#' @rdname day12
#' @param dat data
#' @export
#'
cave_routes <- function(dat) {
  # Initialise routes
  completed_routes <- list()
  unfinished_routes <- dplyr::filter(dat, from == "start")
  unfinished_routes <- lapply(seq_len(nrow(unfinished_routes)),
                              function(x) unname(unlist(unfinished_routes[x,])))

  # Plot routes through cave system
  while (length(unfinished_routes) > 0) {
    this_route <- unfinished_routes[[1]]
    this_cave <- tail(this_route, 1)

    # Record next step(s) of the route
    next_steps <- dplyr::filter(dat, from == this_cave, to != "start")$to

    # If the exit has been found, move the route to `completed_routes`
    if ("end" %in% next_steps) {
      completed_routes <- c(completed_routes, list(c(this_route, "end")))
      next_steps <- setdiff(next_steps, "end")
    }

    # If the cave is small and has already been visited, ignore it
    small <- next_steps[vapply(next_steps, function(x)
      grepl("^[[:lower:]]+$", x), logical(1))]
    big <- setdiff(next_steps, small)
    next_steps <- c(setdiff(small, this_route), big)

    # Record next step(s) of the route
    add_these <- lapply(next_steps, function(x) c(this_route, x))

    # Record steps and tidy up
    unfinished_routes <- c(unfinished_routes, add_these)
    unfinished_routes <- unfinished_routes[-1]
  }
  length(completed_routes)
}