07: Internet Protocol Version 7

library(mistlecode)

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

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

dt <- readLines("input.txt")

Part 1

Ugh. A stupid mistake with my variable scoping and a lot of headaches…

find_char <- function(x, char) {
  x |>
    str_locate_all(char) |>
    unlist() |>
    unique()
}

find_abba <- function(s) {
  any(
    s != lead(s, 1) & s == lead(s, 3) & lead(s, 1) == lead(s, 2), 
    na.rm = TRUE
  )
}

dt |>
  map_lgl(\(x) {
    s <- find_char(x, "\\[")
    e <- find_char(x, "\\]")
    brackets <-
      map2_lgl(s, e, \(s, e) {
        x |>
          substr(s, e) |>
          str_split_1("") |>
          find_abba()
      }) |>
      any()
    if (!brackets) {
      pat <-
        map2_chr(s, e, ~ str_sub(x, .x, .y)) |>
        str_escape() |>
        paste0(collapse = "|")
      x <-
        x |>
        str_replace_all(pat, " ") |>
        str_split_1(" ") |>
        map_lgl(~ find_abba(str_split_1(.x, ""))) |>
        any()
      return(x)
    } else {
      return(FALSE)
    }
  }) |>
  sum()

[1] 110

Part 2

Just not my day today, I guess. Spent a bit of time struggling with vector comparison issues that I couldn’t find.

find_bab <- function(s) {
  w <- which(s != lead(s, 1) & s == lead(s, 2))
  if (length(w) > 0) map(w, ~ paste0(s[.x+1], s[.x], s[.x+1])) else NULL
}

dt |>
  map_lgl(\(x) {
    s <- find_char(x, "\\[")
    e <- find_char(x, "\\]")
    brackets <-
      map2(s, e, \(s, e) {
        x |>
          substr(s, e) |>
          str_split_1("") |>
          find_bab()
      }) |>
      discard(is.null) |>
      unlist() |>
      unique()
    if (length(brackets) > 0) {
      x <-
        brackets |>
        map_lgl(\(aba) {
          pat <-
            map2_chr(s, e, ~ str_sub(x, .x, .y)) |>
            str_escape() |>
            paste0(collapse = "|")
          x |>
            str_replace_all(pat, " ") |>
            str_detect(aba)
        }) |>
        any()
      return(x)
    } else {
      return(FALSE)
    }
  }) |>
  sum()

[1] 242