Day 25

Advent of Code: Worked Solutions

Setup

# Libraries
library(tidyverse)

# Read input from file
input <- read_lines("../input/day25.txt", skip_empty_rows = TRUE)

Part 1

Convert “snafu” strings to decimal numbers:

snafu_to_dbl <- function(snafu) {
  snafu |> 
    str_split("") |> 
    map(~ case_match(rev(.x), "2" ~ 2, "1" ~ 1, "0" ~ 0, "-" ~ -1, "=" ~ -2)) |> 
    map(~ .x * 5^(0:(length(.x) - 1))) |> 
    map_dbl(sum)
}

Convert decimal numbers to “snafu” strings:

dbl_to_snafu <- function(x) {
  output <- c()

  repeat {
    output <- c((x + 2) %% 5 - 2, output)
    x <- floor((x + 2) / 5)
    
    if (x == 0) break
  }
  
  output |> 
    case_match(2 ~ '2', 1 ~ '1', 0 ~ '0', -1 ~ '-', -2 ~ '=') |> 
    str_c(collapse = "")
}

Run on puzzle input:

input |> 
  snafu_to_dbl() |> 
  sum() |> 
  dbl_to_snafu()

[1] "122-12==0-01=00-0=02"