Advent of Code 2021 in R - Day 3

AdventOfCode2021_d03_main.R

library(tidyverse)

binary_flip <- function(x) ifelse(x=="1","0","1")

bits_seq_to_decimal <- function(x) strtoi(paste0(x, collapse = ""), base=2)

# Challenge 1
bits <- readr::read_lines("days/d03/data.txt") %>%
  stringr::str_split("")

most_common <- bits %>%
  purrr::transpose() %>%
  purrr::map(unlist) %>%
  purrr::map(~sort(table(.), decreasing=T)) %>%
  purrr::map(names) %>%
  purrr::map(dplyr::first)

gamma <- bits_seq_to_decimal(most_common)

epsilon <- most_common %>%
  purrr::map(binary_flip) %>%
  bits_seq_to_decimal

gamma * epsilon

# Challenge 2
most_commons_in_col_n <- function(x, n) {
  counts <- purrr::map_chr(x, ~.[n]) %>%
  table() %>%
  sort(decreasing = TRUE)

  ifelse(counts[1] > counts[2], names(counts)[1], "1")
}

o2generator_rating_machine <- function(bits_data, col) {
  pred <- most_commons_in_col_n(bits_data, col)
  keepers <- purrr::keep(bits_data, ~.[col] == pred)
  ifelse(length(keepers) == 1,
         keepers[1],
         o2generator_rating_machine(keepers, col+1))
}

o2binary <- o2generator_rating_machine(bits, 1)
o2_rating <- bits_seq_to_decimal(o2binary[[1]])

co2scrubber_rating_machine <- function(bits_data, col) {
  pred <- binary_flip(most_commons_in_col_n(bits_data, col))
  keepers <- purrr::keep(bits_data, ~.[col] == pred)
  ifelse(length(keepers) == 1,
         keepers,
         co2scrubber_rating_machine(keepers, col+1))
}

co2binary <- co2scrubber_rating_machine(bits, 1)
co2_rating <- bits_seq_to_decimal(co2binary[[1]])

o2_rating * co2_rating