Advent of Code day 2

Part 1

Read in our puzzle input:

day <- 2

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

length(input)

## [1] 2500

Convert to 2 character vectors:

vecs <- input |>
  stringr::str_extract_all("[A-Z]{1}")

player_1 <- purrr::map_chr(vecs, 1)
player_2 <- purrr::map_chr(vecs, 2)

Work out the results / points:

tibble::tibble(
  a = player_1, b = player_2
) |>
  dplyr::mutate(result_points = dplyr::case_when(
    # draws
    a == "A" & b == "X" ~ 3,
    a == "B" & b == "Y" ~ 3,
    a == "C" & b == "Z" ~ 3,
    # a wins
    a == "A" & b == "Z" ~ 0,
    a == "B" & b == "X" ~ 0,
    a == "C" & b == "Y" ~ 0,
    # b wins
    a == "A" & b == "Y" ~ 6,
    a == "B" & b == "Z" ~ 6,
    a == "C" & b == "X" ~ 6
  )) |>
  dplyr::mutate(shape_points = dplyr::case_when(
    b == "X" ~ 1,
    b == "Y" ~ 2,
    b == "Z" ~ 3
  )) |>
  dplyr::summarise(dplyr::across(
    all_of(c("result_points", "shape_points")), sum)) |>
  unlist() |>
  sum()

## [1] 14297

Part 2

tibble::tibble(
  a = player_1, b = player_2
) |>
  dplyr::mutate(shape_points = dplyr::case_when(
    # lose
    a == "A" & b == "X" ~ 3,
    a == "B" & b == "X" ~ 1,
    a == "C" & b == "X" ~ 2,
    # draw
    a == "A" & b == "Y" ~ 1,
    a == "B" & b == "Y" ~ 2,
    a == "C" & b == "Y" ~ 3,
    # win
    a == "A" & b == "Z" ~ 2,
    a == "B" & b == "Z" ~ 3,
    a == "C" & b == "Z" ~ 1
  )) |>
  dplyr::mutate(result_points = dplyr::case_when(
    b == "X" ~ 0,
    b == "Y" ~ 3,
    b == "Z" ~ 6
  )) |>
  dplyr::summarise(dplyr::across(
    all_of(c("result_points", "shape_points")), sum)) |>
  unlist() |>
  sum()

## [1] 10498