day07.md

— Day 7: Handy Haversacks —

Fleur Kelpin Dec 7, 2020

library(tidyverse)
input <- readr::read_lines("day07.txt") %>%
  as_tibble()
input

## # A tibble: 594 x 1
##    value                                                                        
##    <chr>                                                                        
##  1 dark indigo bags contain 2 clear indigo bags.                                
##  2 mirrored gold bags contain 2 pale blue bags, 1 dark violet bag.              
##  3 dim aqua bags contain 1 mirrored beige bag.                                  
##  4 dim fuchsia bags contain 5 dark red bags, 1 muted green bag, 4 clear indigo …
##  5 shiny fuchsia bags contain 4 wavy teal bags, 4 dim cyan bags, 4 light green …
##  6 posh chartreuse bags contain 2 faded blue bags, 2 pale plum bags, 2 posh cor…
##  7 striped red bags contain 3 vibrant red bags.                                 
##  8 striped purple bags contain 5 shiny brown bags.                              
##  9 dark silver bags contain 1 dull aqua bag, 4 dim magenta bags.                
## 10 dark chartreuse bags contain 2 plaid black bags, 4 light bronze bags, 5 dott…
## # … with 584 more rows

Part 1

How many bag colors can eventually contain at least one shiny gold bag?

who_contains <- function(type) {
  input %>%
    extract(value,
      paste0("(.+) bags contain .*", type, " bags?"),
      into = c("container")
    ) %>%
    drop_na() %>%
    {
      .$container
    }
}
who_contains("shiny gold")

## [1] "plaid gold"    "bright violet" "clear brown"   "clear blue"   
## [5] "faded gold"    "drab purple"

all_contains <- function(containers, checked) {
  new_containers <- containers %>%
    map(who_contains) %>%
    unlist() %>%
    unique() %>%
    setdiff(checked)
  num_found <- length(new_containers)
  if (num_found == 0) {
    return(0)
  }
  length(new_containers) + all_contains(
    new_containers,
    unique(c(
      checked,
      containers,
      new_containers
    ))
  )
}
all_contains("shiny gold", c())

## [1] 233

Part 2

How many individual bags are required inside your single shiny gold bag?

contents <- function(type) {
  inside <- input %>%
    extract(value, paste0(type, " bags contain (.*)"), into = "line") %>%
    separate_rows(line, sep = ",") %>%
    extract(line,
      "(\\d+) (.*) bags?",
      convert = TRUE, into = c("num", "type")
    ) %>%
    drop_na()
  if (nrow(inside) == 0) {
    return(0)
  }
  inside %>%
    rowwise() %>%
    mutate(total = num + num * contents(type)) %>%
    {
      sum(.$total)
    }
}

contents("shiny gold")

## [1] 421550