Advent of Code 2021 in R - Day 2

AdventOfCode2021_d02_main.R

library(tidyverse)

input <- readr::read_lines("days/d02/data.txt") %>%
  stringr::str_split(" ")

# Challenge 1
hor <- input %>%
  purrr::keep(~ .[1] == "forward") %>%
  purrr::map_dbl(~as.numeric(.[2])) %>%
  sum

dep <- input %>%
  purrr::discard(~ .[1] == "forward") %>%
  purrr::map_dbl(~ ifelse(.[1] == "down", as.numeric(.[2]), -as.numeric(.[2]))) %>%
  sum

hor * dep

# Challenge 2
gps <- input %>%
  purrr::reduce(function(acc, nxt) {
    x <- as.numeric(nxt[2])
    if (nxt[1] == "down") {
      purrr::list_modify(acc, aim=acc$aim + x)
    } else if (nxt[1] == "up") {
      purrr::list_modify(acc, aim=acc$aim - x)
    } else {
      purrr::list_modify(acc, depth=acc$depth + acc$aim * x, hor=acc$hor + x)
    }
  }, .init = list(aim=0, depth=0, hor=0))

gps$depth * gps$hor

# Challenge 2 with S3
update_state <- function(current, x) {
  UseMethod("update_state", x)
}
update_state.forward <- function(current, x) {
  purrr::list_modify(current, 
                     depth=current$depth + current$aim * unclass(x), 
                     hor=current$hor + unclass(x))
}
update_state.up <- function(current, x) {
  purrr::list_modify(current, aim=current$aim - unclass(x))
}
update_state.down <- function(current, x) {
  purrr::list_modify(current, aim=current$aim + unclass(x))
}
input %>% 
  purrr::map(~structure(as.numeric(.[2]), class=.[1])) %>% 
  purrr::reduce(update_state, 
                .init = list(aim=0, depth=0, hor=0)) %>% 
  with(depth * hor)