Day 7

Advent of Code: Worked Solutions

Setup

# Libraries
library(tidyverse)

# Read input from file
input <- read_lines("../input/day07.txt") |> 
  enframe(name = NULL)

Part 1

dir_sizes <- input |> 
  mutate(

    # Determine path of each file by accumulating preceding cd terms
    path = value |>
      str_extract("(?<=^\\$ cd ).*") |>
      str_c("/") |>
      replace_na("") |>
      accumulate(
        ~ if (.y == "../") {
          str_remove(.x, "(?<=/)[a-z]+/$")
        } else {
          str_c(.x, .y)
        }
      ) |>
      str_remove_all("^/|/$"),

    # Convert paths to lists of all containing directories
    dirs = path |>
      str_split("/") |>
      map(~accumulate(.x, str_c, sep = "/"))
  ) |>

  # Remove commands & directories from output and format file info as cols
  filter(!str_detect(value, "^\\$|dir ")) |>
  separate(value, into = c("size", "file"), sep = " ") |>
  mutate(size = as.integer(size)) |>

  # Convert nested lists of directories to long-format
  unnest_wider(dirs, names_sep = "_") |>
  mutate(dirs_1 = "/") |>
  pivot_longer(
    cols = matches("dirs_\\d+"),
    names_to = NULL,
    values_to = "dir",
    values_drop_na = TRUE
  ) |>

  # Compute size of each directory
  group_by(dir) |>
  summarize(size = sum(size)) |>
  ungroup()

Sum sizes of all directories with maximum size 100000:

dir_sizes |>
  filter(size <= 100000) |>
  pull(size) |>
  sum()

[1] 1243729

Part 2

Find size of the smallest necessary directory to delete:

curr_system_size <- dir_sizes |>
  filter(dir == "/") |>
  pull(size)

dir_sizes |>
  filter(size >= (30000000 - (70000000 - curr_system_size))) |>
  slice_min(size) |>
  pull(size)

[1] 4443914