Day 4

Advent of Code: Worked Solutions

Setup

Import libraries:

library(tidyverse)
library(unglue)

Read text input from file and separate into lists of key-value pairs:

input <- read_lines("../input/day04.txt")

Part 1

Convert text input to a data frame of key value-pairs, enumerated according to the blank lines, and determine whether each passport has all requied fields (ignoring “cid”):

byr (Birth Year)
iyr (Issue Year)
eyr (Expiration Year)
hgt (Height)
hcl (Hair Color)
ecl (Eye Color)
pid (Passport ID)
cid (Country ID)

required_keys <- c("byr", "iyr", "eyr", "hgt", "hcl", "ecl", "pid")

df <- input |> 
  
  # Convert text lines to data frame
  str_flatten(collapse = "\n") |> 
  str_split_1("\n\n") |> 
  str_split("\\s") |> 
  imap_dfr(\(str, idx) {
    str |> 
      unglue_data("{key}:{value}") |> 
      mutate(idx = idx)
  }) |> 
  
  # Flag whether each passpord is valid or not
  mutate(
    is_valid = sum(key %in% required_keys) == 7, 
    .by = idx
  )

Count the total valid passpords:

df |> 
  filter(is_valid) |> 
  distinct(idx) |> 
  nrow()

Part 2

Filter to the passports with all required fields, validate those fields, and count the final number of valid results:

df |> 
  filter(is_valid & key %in% required_keys) |> 
  mutate(
    is_valid = (
      (
        key == "byr" 
          & str_length(value) == 4 
          & between(parse_number(value), 1920, 2002)
      ) | (
        key == "iyr" 
          & str_length(value) == 4 
          & between(parse_number(value), 2010, 2020)
      ) | (
        key == "eyr" 
          & str_length(value) == 4 
          & between(parse_number(value), 2020, 2030)
      ) | (
        key == "hgt" 
          & str_detect(value, "^\\d+cm$")
          & between(parse_number(value), 150, 193)
      ) | (
        key == "hgt" 
          & str_detect(value, "^\\d+in$")
          & between(parse_number(value), 59, 76)
      ) | (
        key == "hcl" 
          & str_detect(value, "^#[0-9a-f]{6}$")
      ) | (
        key == "ecl" 
          & value %in% c("amb", "blu", "brn", "gry", "grn", "hzl", "oth")
      ) | (
        key == "pid" 
          & str_detect(value, "^\\d{9}$")
      )
    )
  ) |> 
  filter(all(is_valid), .by = idx) |> 
  distinct(idx) |> 
  nrow()