Day 5

Advent of Code: Worked Solutions

Setup

Import libraries:

library(tidyverse)
library(unglue)

Read text input from file and separate the row segment of each string from the column seegment:

input <- read_lines("../input/day05.txt") |> 
  unglue_data("{row=[FB]+}{col=[LR]+}")

Part 1

Each F/B or R/L pair can be treated as a binary string. Replace F and L with 0, replace B and R with 1, and compute the result:

bin <- c("F" = "0", "B" = "1", "L" = "0", "R" = "1")

df <- input |> 
  mutate(
    across(everything(), ~ strtoi(str_replace_all(.x, bin), base = 2L)),
    seat_id = row * 8 + col
  )

Get the maximum seat ID:

max(df$seat_id)

Part 2

Find the missing value within the range of all seat IDs:

setdiff(min(df$seat_id):max(df$seat_id), df$seat_id)