90 lines
3.4 KiB
Plaintext
90 lines
3.4 KiB
Plaintext
|
Advent of Code
|
|||
|
|
|
|||
|
|
--- Day 8: Two-Factor Authentication ---
|
|||
|
|
|
|||
|
|
You come across a door implementing what you can only assume is an implementation of two-factor authentication
|
|||
|
|
after a long game of requirements telephone.
|
|||
|
|
|
|||
|
|
To get past the door, you first swipe a keycard (no problem; there was one on a nearby desk). Then, it displays a
|
|||
|
|
code on a little screen, and you type that code on a keypad. Then, presumably, the door unlocks.
|
|||
|
|
|
|||
|
|
Unfortunately, the screen has been smashed. After a few minutes, you've taken everything apart and figured out how
|
|||
|
|
it works. Now you just have to work out what the screen would have displayed.
|
|||
|
|
|
|||
|
|
The magnetic strip on the card you swiped encodes a series of instructions for the screen; these instructions are
|
|||
|
|
your puzzle input. The screen is 50 pixels wide and 6 pixels tall, all of which start off, and is capable of three
|
|||
|
|
somewhat peculiar operations:
|
|||
|
|
|
|||
|
|
• rect AxB turns on all of the pixels in a rectangle at the top-left of the screen which is A wide and B tall.
|
|||
|
|
• rotate row y=A by B shifts all of the pixels in row A (0 is the top row) right by B pixels. Pixels that would
|
|||
|
|
fall off the right end appear at the left end of the row.
|
|||
|
|
• rotate column x=A by B shifts all of the pixels in column A (0 is the left column) down by B pixels. Pixels
|
|||
|
|
that would fall off the bottom appear at the top of the column.
|
|||
|
|
|
|||
|
|
For example, here is a simple sequence on a smaller screen:
|
|||
|
|
|
|||
|
|
• rect 3x2 creates a small rectangle in the top-left corner:
|
|||
|
|
|
|||
|
|
###....
|
|||
|
|
###....
|
|||
|
|
.......
|
|||
|
|
|
|||
|
|
• rotate column x=1 by 1 rotates the second column down by one pixel:
|
|||
|
|
|
|||
|
|
#.#....
|
|||
|
|
###....
|
|||
|
|
.#.....
|
|||
|
|
|
|||
|
|
• rotate row y=0 by 4 rotates the top row right by four pixels:
|
|||
|
|
|
|||
|
|
....#.#
|
|||
|
|
###....
|
|||
|
|
.#.....
|
|||
|
|
|
|||
|
|
• rotate column x=1 by 1 again rotates the second column down by one pixel, causing the bottom pixel to wrap back
|
|||
|
|
to the top:
|
|||
|
|
|
|||
|
|
.#..#.#
|
|||
|
|
#.#....
|
|||
|
|
.#.....
|
|||
|
|
|
|||
|
|
As you can see, this display technology is extremely powerful, and will soon dominate the
|
|||
|
|
tiny-code-displaying-screen market. That's what the advertisement on the back of the display tries to convince you,
|
|||
|
|
anyway.
|
|||
|
|
|
|||
|
|
There seems to be an intermediate check of the voltage used by the display: after you swipe your card, if the
|
|||
|
|
screen did work, how many pixels should be lit?
|
|||
|
|
|
|||
|
|
Your puzzle answer was _____.
|
|||
|
|
|
|||
|
|
--- Part Two ---
|
|||
|
|
|
|||
|
|
You notice that the screen is only capable of displaying capital letters; in the font it uses, each letter is 5
|
|||
|
|
pixels wide and 6 tall.
|
|||
|
|
|
|||
|
|
After you swipe your card, what code is the screen trying to display?
|
|||
|
|
|
|||
|
|
Your puzzle answer was _____________.
|
|||
|
|
|
|||
|
|
References
|
|||
|
|
|
|||
|
|
Visible links
|
|||
|
|
. http://adventofcode.com/
|
|||
|
|
. http://adventofcode.com/2016/about
|
|||
|
|
. http://adventofcode.com/2016/support
|
|||
|
|
. http://adventofcode.com/2016/events
|
|||
|
|
. http://adventofcode.com/2016/settings
|
|||
|
|
. http://adventofcode.com/2016/auth/logout
|
|||
|
|
. http://adventofcode.com/2016
|
|||
|
|
. http://adventofcode.com/2016
|
|||
|
|
. http://adventofcode.com/2016/leaderboard
|
|||
|
|
. http://adventofcode.com/2016/stats
|
|||
|
|
. http://adventofcode.com/2016/sponsors
|
|||
|
|
. http://adventofcode.com/2016/sponsors
|
|||
|
|
. https://en.wikipedia.org/wiki/Multi-factor_authentication
|
|||
|
|
. https://en.wikipedia.org/wiki/Requirement
|
|||
|
|
. https://en.wikipedia.org/wiki/Chinese_whispers
|
|||
|
|
. https://www.google.com/search?q=tiny+lcd&tbm=isch
|
|||
|
|
. http://adventofcode.com/2016
|
|||
|
|
. http://adventofcode.com/2016/day/8/input
|