01: Inverse Captcha

library(data.table)
library(magrittr)

dt <- readLines("input.txt") |>
  strsplit("") |>
  unlist() |>
  as.numeric()

Part 1

data.table(
  "input" = c(dt),
  "test" = c(dt[-1], dt[1])
) %>%
  .[, "valid" := ifelse(input == test, TRUE, FALSE)] %>%
  .[valid == TRUE, test] %>%
  sum()

[1] 1031

Part 2

len <- length(dt) / 2
data.table(
  "input" = c(dt),
  "test" = c(dt[(len + 1):length(dt)], dt[1:len])
) %>%
  .[, "valid" := ifelse(input == test, TRUE, FALSE)] %>%
  .[valid == TRUE, test] %>%
  sum()

[1] 1080