92 lines
2.7 KiB
Org Mode
92 lines
2.7 KiB
Org Mode
** --- Day 5: Supply Stacks ---
|
|
The expedition can depart as soon as the final supplies have been
|
|
unloaded from the ships. Supplies are stored in stacks of marked
|
|
/crates/, but because the needed supplies are buried under many other
|
|
crates, the crates need to be rearranged.
|
|
|
|
The ship has a /giant cargo crane/ capable of moving crates between
|
|
stacks. To ensure none of the crates get crushed or fall over, the crane
|
|
operator will rearrange them in a series of carefully-planned steps.
|
|
After the crates are rearranged, the desired crates will be at the top
|
|
of each stack.
|
|
|
|
The Elves don't want to interrupt the crane operator during this
|
|
delicate procedure, but they forgot to ask her /which/ crate will end up
|
|
where, and they want to be ready to unload them as soon as possible so
|
|
they can embark.
|
|
|
|
They do, however, have a drawing of the starting stacks of crates /and/
|
|
the rearrangement procedure (your puzzle input). For example:
|
|
|
|
#+begin_example
|
|
[D]
|
|
[N] [C]
|
|
[Z] [M] [P]
|
|
1 2 3
|
|
|
|
move 1 from 2 to 1
|
|
move 3 from 1 to 3
|
|
move 2 from 2 to 1
|
|
move 1 from 1 to 2
|
|
#+end_example
|
|
|
|
In this example, there are three stacks of crates. Stack 1 contains two
|
|
crates: crate =Z= is on the bottom, and crate =N= is on top. Stack 2
|
|
contains three crates; from bottom to top, they are crates =M=, =C=, and
|
|
=D=. Finally, stack 3 contains a single crate, =P=.
|
|
|
|
Then, the rearrangement procedure is given. In each step of the
|
|
procedure, a quantity of crates is moved from one stack to a different
|
|
stack. In the first step of the above rearrangement procedure, one crate
|
|
is moved from stack 2 to stack 1, resulting in this configuration:
|
|
|
|
#+begin_example
|
|
[D]
|
|
[N] [C]
|
|
[Z] [M] [P]
|
|
1 2 3
|
|
#+end_example
|
|
|
|
In the second step, three crates are moved from stack 1 to stack 3.
|
|
Crates are moved /one at a time/, so the first crate to be moved (=D=)
|
|
ends up below the second and third crates:
|
|
|
|
#+begin_example
|
|
[Z]
|
|
[N]
|
|
[C] [D]
|
|
[M] [P]
|
|
1 2 3
|
|
#+end_example
|
|
|
|
Then, both crates are moved from stack 2 to stack 1. Again, because
|
|
crates are moved /one at a time/, crate =C= ends up below crate =M=:
|
|
|
|
#+begin_example
|
|
[Z]
|
|
[N]
|
|
[M] [D]
|
|
[C] [P]
|
|
1 2 3
|
|
#+end_example
|
|
|
|
Finally, one crate is moved from stack 1 to stack 2:
|
|
|
|
#+begin_example
|
|
[Z]
|
|
[N]
|
|
[D]
|
|
[C] [M] [P]
|
|
1 2 3
|
|
#+end_example
|
|
|
|
The Elves just need to know /which crate will end up on top of each
|
|
stack/; in this example, the top crates are =C= in stack 1, =M= in stack
|
|
2, and =Z= in stack 3, so you should combine these together and give the
|
|
Elves the message =CMZ=.
|
|
|
|
/After the rearrangement procedure completes, what crate ends up on top
|
|
of each stack?/
|
|
|
|
To begin, [[file:5/input][get your puzzle input]].
|