Part 1

Read in our puzzle input:

day <- 6

input <- here::here(
  "2022", "input",
  paste0("day_", stringr::str_pad(day, 2, "left", "0"))
  ) |>
  readLines()


test_inputs <- c(
  "mjqjpqmgbljsphdztnvjfqwrcgsmlb",
  "bvwbjplbgvbhsrlpgdmjqwftvncz",
  "nppdvjthqldpwncqszvftbrmjlhg",
  "nznrnfrfntjfmvfwmzdfjlvtqnbhcprsg",
  "zcfzfwzzqfrljwzlrfnpqdbhtmscgvjw"
)

test_answers <- c(7, 5, 6, 10, 11)

check_marker <- function(buffer, n = 4) {
    stopifnot("n is beyond the length of the buffer" = n <= length(buffer))

    if (length(unique(buffer[(n-3):n])) < 4) {
      check_marker(buffer, n + 1)
    } else n
  }


check_marker(unlist(strsplit(test_inputs[1], ""))) == test_answers[1] &
check_marker(unlist(strsplit(test_inputs[2], ""))) == test_answers[2] & 
check_marker(unlist(strsplit(test_inputs[3], ""))) == test_answers[3] & 
check_marker(unlist(strsplit(test_inputs[4], ""))) == test_answers[4] & 
check_marker(unlist(strsplit(test_inputs[5], ""))) == test_answers[5]

## [1] TRUE

strsplit(input, "") |>
  unlist() |>
  check_marker()

## [1] 1912

Part 2

test_answers2 <- c(19, 23, 23, 29, 26)

check_marker2 <- function(buffer, n = 14) {
    stopifnot("n is beyond the length of the buffer" = n <= length(buffer))

    if (length(unique(buffer[(n-13):n])) < 14) {
      check_marker2(buffer, n + 1)
    } else n
  }

check_marker2(unlist(strsplit(test_inputs[1], ""))) == test_answers2[1] &
check_marker2(unlist(strsplit(test_inputs[2], ""))) == test_answers2[2] & 
check_marker2(unlist(strsplit(test_inputs[3], ""))) == test_answers2[3] & 
check_marker2(unlist(strsplit(test_inputs[4], ""))) == test_answers2[4] & 
check_marker2(unlist(strsplit(test_inputs[5], ""))) == test_answers2[5]

## [1] TRUE

strsplit(input, "") |>
  unlist() |>
  check_marker2()

## [1] 2122