R/12-2.R

In soniamitchell/adventofcode: My Advent of Code solutions

#' @rdname day12
#' @export
#'
cave_routes2 <- function(dat) {
  # Initialise routes
  unfinished <- dplyr::filter(dat, from == "start")
  complete <- data.frame()

  last_step <- "to"

  # Plot routes through cave system
  while (nrow(unfinished) != 0) {
    # Record next step(s) of the route
    unfinished <- dplyr::left_join(unfinished, dat,
                                   by = setNames("from", last_step))

    # Extract column name of the last step
    last_step <- tail(names(unfinished), 1)

    # For each unfinished route, count the number of small caves that were
    # visited more than once
    test <- apply(unfinished, 1, function(x) {
      duplicates <- x[duplicated(unlist(x))]
      islower <- grepl("^[[:lower:]]+$", duplicates)
      sum(islower)})
    # Remove routes where more than one small cave was visited more than once
    index <- which(test > 1)
    if (length(index) > 0)
      unfinished <- unfinished[-index, ]

    # Add completed routes to `complete`
    complete <- dplyr::bind_rows(complete,
                                 dplyr::filter(unfinished,
                                               get(last_step) == "end"))

    # Remove completed routes from `unfinished`
    unfinished <- dplyr::filter(unfinished, get(last_step) != "end")
  }
  nrow(complete)
}