R/3-1.R

In soniamitchell/adventofcode: My Advent of Code solutions

#' Day 3: Binary Diagnostic
#' @source <https://adventofcode.com/2021/day/3>
#' @name day3
#'
NULL

#' @rdname day3
#' @param path file path
#' @export
#'
read_day3 <- function(path) {
  path |>
    scan(what = "character")
}

#' @rdname day3
#' @param dat dat
#' @export
#'
power_consumption <- function(dat) {
  # Number of bits in each binary number
  digits <- nchar(dat[1])

  # Calculate gamma and epsilon rates
  gamma_binary <- rep(NA, digits)
  epsilon_binary <- rep(NA, digits)

  for (i in seq_len(digits)) {
    # Extract the i[th] character of each string
    character <- vapply(dat, function(x) substr(x, i, i), character(1))
    # Find most common bit
    zeroes <- sum(character == "0")
    ones <- sum(character == "1")
    gamma_binary[i] <- dplyr::if_else(zeroes > ones, 0, 1)
    epsilon_binary[i] <- dplyr::if_else(zeroes < ones, 0, 1)
  }

  gamma_rate <- strtoi(paste(gamma_binary, collapse = ""), base = 2)
  epsilon_rate <- strtoi(paste(epsilon_binary, collapse = ""), base = 2)

  # Calculate power consumption
  gamma_rate * epsilon_rate
}