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Brian Buller
2018-03-15 11:24:23 -05:00
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@@ -2,24 +2,33 @@ 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.
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.
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.
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:
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.
• 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:
@@ -41,30 +50,31 @@ Advent of Code
###....
.#.....
• 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:
• 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.
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?
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 _____.
Your puzzle answer was 119.
--- 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.
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 _____________.
Your puzzle answer was ZFHFSFOGPO.
References