10: Elves Look, Elves Say

library(mistlecode)

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

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

library(progressr)
dt <- "1113222113"

Part 1

I got stuck trying to think of the smart way to do this so I’m brute-forcing it with recursion instead.

expand <- function(x, max, i = 1) {
  if (i == (max + 1)) { return(nchar(x)) }
  x <-
    x |>
    strsplit("") |>
    unlist() |>
    data.table() |>
    `colnames<-`("input") |>
    mutate(group = rleid(input)) |>
    group_by(group, input) |>
    summarise(count = n(), .groups = "drop") |>
    mutate(string = glue::glue("{count}{input}")) |>
    pull(string) |>
    paste0(collapse = "")
  p()
  return(expand(x, max, i + 1))
}

times <- 40
with_progress({ 
  p <- progressor(steps = times)
  expand(dt, times) 
})

[1] 252594

Part 2

I thought it was going to be 100 iterations. I can’t believe I’m glad for just 50… But I think I can brute-force this too. I definitely have enough RAM. I just modified the function a bit to take a max iteration input argument as well.

times <- 50
with_progress({ 
  p <- progressor(steps = times)
  expand(dt, times) 
})

[1] 3579328