R/21-1.R

In soniamitchell/adventofcode: My Advent of Code solutions

#' Day 21: Dirac Dice
#' @source <https://adventofcode.com/2021/day/21>
#' @name day21
#'
NULL

#' @rdname day21
#' @param path file path
#' @export
#'
read_day21 <- function(path) {
  path |>
    readLines()
}

#' @rdname day21
#' @param dat dat
#' @export
#'
deterministic <- function(dat) {
  start <- dat |>
    vapply(function(x) gsub(".*([0-9])$", "\\1", x),
           character(1)) |>
    as.numeric()

  pos1 <- start[1]
  pos2 <- start[2]
  score1 <- 0
  score2 <- 0
  i <- 0

  while (all(c(score1, score2) < 1000)) {
    i <- i + 1

    if (i%%2 != 0) {
      pos1 <- pos1 + sum(((i * 3) - 2):(i * 3))
      pos1 <- dplyr::if_else(pos1 > 10, pos1%%10, pos1)
      pos1 <- dplyr::if_else(pos1 == 0, 10, pos1) # since pos1 = 100 returns 0
      score1 <- score1 + pos1

    } else {
      pos2 <- pos2 + sum(((i * 3) - 2):(i * 3))
      pos2 <- dplyr::if_else(pos2 > 10, pos2%%10, pos2)
      pos2 <- dplyr::if_else(pos2 == 0, 10, pos2)
      score2 <- score2 + pos2
    }
  }

  min(score1, score2) * i * 3
}