2022 day 7 init

2022/day07/README.org

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+** --- Day 7: No Space Left On Device ---
+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?
+
+The device the Elves gave you has problems with more than just its
+communication system. You try to run a system update:
+
+#+begin_example
+$ system-update --please --pretty-please-with-sugar-on-top
+Error: No space left on device
+#+end_example
+
+Perhaps you can delete some files to make space for the update?
+
+You browse around the filesystem to assess the situation and save the
+resulting terminal output (your puzzle input). For example:
+
+#+begin_example
+$ cd /
+$ ls
+dir a
+14848514 b.txt
+8504156 c.dat
+dir d
+$ cd a
+$ ls
+dir e
+29116 f
+2557 g
+62596 h.lst
+$ cd e
+$ ls
+584 i
+$ cd ..
+$ cd ..
+$ cd d
+$ ls
+4060174 j
+8033020 d.log
+5626152 d.ext
+7214296 k
+#+end_example
+
+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.
+
+Within the terminal output, lines that begin with =$= are /commands you
+executed/, very much like some modern computers:
+
+- =cd= means /change directory/. This changes which directory is the
+  current directory, but the specific result depends on the argument:
+  - =cd x= moves /in/ one level: it looks in the current directory for
+    the directory named =x= and makes it the current directory.
+  - =cd ..= moves /out/ one level: it finds the directory that contains
+    the current directory, then makes that directory the current
+    directory.
+  - =cd /= switches the current directory to the outermost directory,
+    =/=.
+- =ls= means /list/. It prints out all of the files and directories
+  immediately contained by the current directory:
+  - =123 abc= means that the current directory contains a file named
+    =abc= with size =123=.
+  - =dir xyz= means that the current directory contains a directory
+    named =xyz=.
+
+Given the commands and output in the example above, you can determine
+that the filesystem looks visually like this:
+
+#+begin_example
+- / (dir)
+  - a (dir)
+    - e (dir)
+      - i (file, size=584)
+    - f (file, size=29116)
+    - g (file, size=2557)
+    - h.lst (file, size=62596)
+  - b.txt (file, size=14848514)
+  - c.dat (file, size=8504156)
+  - d (dir)
+    - j (file, size=4060174)
+    - d.log (file, size=8033020)
+    - d.ext (file, size=5626152)
+    - k (file, size=7214296)
+#+end_example
+
+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.
+
+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.)
+
+The total sizes of the directories above can be found as follows:
+
+- The total size of directory =e= is /584/ because it contains a single
+  file =i= of size 584 and no other directories.
+- 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=).
+- Directory =d= has total size /24933642/.
+- As the outermost directory, =/= contains every file. Its total size is
+  /48381165/, the sum of the size of every file.
+
+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!)
+
+Find all of the directories with a total size of at most 100000. /What
+is the sum of the total sizes of those directories?/
+
+To begin, [[file:7/input][get your puzzle input]].
+
+Answer:
+
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