105 lines
No EOL
5.3 KiB
Markdown
105 lines
No EOL
5.3 KiB
Markdown
# Day 7: No Space Left On Device
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You can hear birds chirping and raindrops hitting leaves as the expedition proceeds. Occasionally, you can even hear much louder sounds in the distance; how big do the animals get out here, anyway?
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The device the Elves gave you has problems with more than just its communication system. You try to run a system update:
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```
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$ system-update --please --pretty-please-with-sugar-on-top
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Error: No space left on device
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```
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Perhaps you can delete some files to make space for the update?
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You browse around the filesystem to assess the situation and save the resulting terminal output (your puzzle input). For example:
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```
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$ cd /
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$ ls
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dir a
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14848514 b.txt
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8504156 c.dat
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dir d
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$ cd a
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$ ls
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dir e
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29116 f
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2557 g
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62596 h.lst
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$ cd e
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$ ls
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584 i
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$ cd ..
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$ cd ..
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$ cd d
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$ ls
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4060174 j
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8033020 d.log
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5626152 d.ext
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7214296 k
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```
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The filesystem consists of a tree of files (plain data) and directories (which can contain other directories or files). The outermost directory is called `/`. You can navigate around the filesystem, moving into or out of directories and listing the contents of the directory you're currently in.
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Within the terminal output, lines that begin with `$` are *commands you executed*, very much like some modern computers:
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- `cd` means *change directory*. This changes which directory is the current directory, but the specific result depends on the argument:
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- `cd x` moves *in* one level: it looks in the current directory for the directory named `x` and makes it the current directory.
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- `cd ..` moves *out* one level: it finds the directory that contains the current directory, then makes that directory the current directory.
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- `cd /` switches the current directory to the outermost directory, `/`.
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- `ls` means *list*. It prints out all of the files and directories immediately contained by the current directory:
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- `123 abc` means that the current directory contains a file named abc with size `123`.
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- `dir xyz` means that the current directory contains a directory named `xyz`.
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Given the commands and output in the example above, you can determine that the filesystem looks visually like this:
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```
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- / (dir)
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- a (dir)
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- e (dir)
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- i (file, size=584)
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- f (file, size=29116)
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- g (file, size=2557)
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- h.lst (file, size=62596)
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- b.txt (file, size=14848514)
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- c.dat (file, size=8504156)
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- d (dir)
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- j (file, size=4060174)
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- d.log (file, size=8033020)
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- d.ext (file, size=5626152)
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- k (file, size=7214296)
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```
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Here, there are four directories: `/` (the outermost directory), `a` and `d` (which are in `/`), and `e` (which is in `a`). These directories also contain files of various sizes.
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Since the disk is full, your first step should probably be to find directories that are good candidates for deletion. To do this, you need to determine the *total size* of each directory. The total size of a directory is the sum of the sizes of the files it contains, directly or indirectly. (Directories themselves do not count as having any intrinsic size.)
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The total sizes of the directories above can be found as follows:
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- The total size of directory `e` is *`584`* because it contains a single file `i` of size 584 and no other directories.
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- The directory `a` has total size *`94853`* because it contains files `f` (size 29116), `g` (size 2557), and `h.lst` (size 62596), plus file `i` indirectly (`a` contains `e` which contains `i`).
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- Directory `d` has total size *`24933642`*.
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- As the outermost directory, `/` contains every file. Its total size is *`48381165`*, the sum of the size of every file.
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To begin, find all of the directories with a total size of *`at most 100000`*, then calculate the sum of their total sizes. In the example above, these directories are a and e; the sum of their total sizes is *`95437`* (94853 + 584). (As in this example, this process can count files more than once!)
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Find all of the directories with a total size of at most 100000. *What is the sum of the total sizes of those directories?*
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## Part 2
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Now, you're ready to choose a directory to delete.
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The total disk space available to the filesystem is *`70000000`*. To run the update, you need unused space of at least *`30000000`*. You need to find a directory you can delete that will *free up enough space* to run the update.
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In the example above, the total size of the outermost directory (and thus the total amount of used space) is `48381165`; this means that the size of the *unused* space must currently be `21618835`, which isn't quite the `30000000` required by the update. Therefore, the update still requires a directory with total size of at least `8381165` to be deleted before it can run.
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To achieve this, you have the following options:
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- Delete directory `e`, which would increase unused space by `584`.
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- Delete directory `a`, which would increase unused space by `94853`.
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- Delete directory `d`, which would increase unused space by `24933642`.
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- Delete directory `/`, which would increase unused space by `48381165`.
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Directories `e` and `a` are both too small; deleting them would not free up enough space. However, directories `d` and `/` are both big enough! Between these, choose the *smallest*: `d`, increasing unused space by `24933642`.
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Find the smallest directory that, if deleted, would free up enough space on the filesystem to run the update. *What is the total size of that directory?* |