223 lines
7.1 KiB
Plaintext
223 lines
7.1 KiB
Plaintext
|
[1]Advent of Code
|
|||
|
|
|
|||
|
|
• [2][About]
|
|||
|
|
• [3][Events]
|
|||
|
|
• [4][Shop]
|
|||
|
|
• [5][Settings]
|
|||
|
|
• [6][Log Out]
|
|||
|
|
|
|||
|
|
br0xen [7](AoC++) 26*
|
|||
|
|
|
|||
|
|
/*[8]2023*/
|
|||
|
|
|
|||
|
|
• [9][Calendar]
|
|||
|
|
• [10][AoC++]
|
|||
|
|
• [11][Sponsors]
|
|||
|
|
• [12][Leaderboard]
|
|||
|
|
• [13][Stats]
|
|||
|
|
|
|||
|
|
Our [14]sponsors help make Advent of Code possible:
|
|||
|
|
[15]Jane Street - Will our next great idea come from you? We hire smart,
|
|||
|
|
humble people who love to solve problems, build systems, and test
|
|||
|
|
theories. Our success is driven by our people and we never stop improving.
|
|||
|
|
|
|||
|
|
--- Day 13: Point of Incidence ---
|
|||
|
|
|
|||
|
|
With your help, the hot springs team locates an appropriate spring which
|
|||
|
|
launches you neatly and precisely up to the edge of Lava Island.
|
|||
|
|
|
|||
|
|
There's just one problem: you don't see any lava.
|
|||
|
|
|
|||
|
|
You do see a lot of ash and igneous rock; there are even what look like
|
|||
|
|
gray mountains scattered around. After a while, you make your way to a
|
|||
|
|
nearby cluster of mountains only to discover that the valley between them
|
|||
|
|
is completely full of large mirrors. Most of the mirrors seem to be
|
|||
|
|
aligned in a consistent way; perhaps you should head in that direction?
|
|||
|
|
|
|||
|
|
As you move through the valley of mirrors, you find that several of them
|
|||
|
|
have fallen from the large metal frames keeping them in place. The mirrors
|
|||
|
|
are extremely flat and shiny, and many of the fallen mirrors have lodged
|
|||
|
|
into the ash at strange angles. Because the terrain is all one color, it's
|
|||
|
|
hard to tell where it's safe to walk or where you're about to run into a
|
|||
|
|
mirror.
|
|||
|
|
|
|||
|
|
You note down the patterns of ash (.) and rocks (#) that you see as you
|
|||
|
|
walk (your puzzle input); perhaps by carefully analyzing these patterns,
|
|||
|
|
you can figure out where the mirrors are!
|
|||
|
|
|
|||
|
|
For example:
|
|||
|
|
|
|||
|
|
#.##..##.
|
|||
|
|
..#.##.#.
|
|||
|
|
##......#
|
|||
|
|
##......#
|
|||
|
|
..#.##.#.
|
|||
|
|
..##..##.
|
|||
|
|
#.#.##.#.
|
|||
|
|
|
|||
|
|
#...##..#
|
|||
|
|
#....#..#
|
|||
|
|
..##..###
|
|||
|
|
#####.##.
|
|||
|
|
#####.##.
|
|||
|
|
..##..###
|
|||
|
|
#....#..#
|
|||
|
|
|
|||
|
|
To find the reflection in each pattern, you need to find a perfect
|
|||
|
|
reflection across either a horizontal line between two rows or across a
|
|||
|
|
vertical line between two columns.
|
|||
|
|
|
|||
|
|
In the first pattern, the reflection is across a vertical line between two
|
|||
|
|
columns; arrows on each of the two columns point at the line between the
|
|||
|
|
columns:
|
|||
|
|
|
|||
|
|
123456789
|
|||
|
|
><
|
|||
|
|
#.##..##.
|
|||
|
|
..#.##.#.
|
|||
|
|
##......#
|
|||
|
|
##......#
|
|||
|
|
..#.##.#.
|
|||
|
|
..##..##.
|
|||
|
|
#.#.##.#.
|
|||
|
|
><
|
|||
|
|
123456789
|
|||
|
|
|
|||
|
|
In this pattern, the line of reflection is the vertical line between
|
|||
|
|
columns 5 and 6. Because the vertical line is not perfectly in the middle
|
|||
|
|
of the pattern, part of the pattern (column 1) has nowhere to reflect onto
|
|||
|
|
and can be ignored; every other column has a reflected column within the
|
|||
|
|
pattern and must match exactly: column 2 matches column 9, column 3
|
|||
|
|
matches 8, 4 matches 7, and 5 matches 6.
|
|||
|
|
|
|||
|
|
The second pattern reflects across a horizontal line instead:
|
|||
|
|
|
|||
|
|
1 #...##..# 1
|
|||
|
|
2 #....#..# 2
|
|||
|
|
3 ..##..### 3
|
|||
|
|
4v#####.##.v4
|
|||
|
|
5^#####.##.^5
|
|||
|
|
6 ..##..### 6
|
|||
|
|
7 #....#..# 7
|
|||
|
|
|
|||
|
|
This pattern reflects across the horizontal line between rows 4 and 5. Row
|
|||
|
|
1 would reflect with a hypothetical row 8, but since that's not in the
|
|||
|
|
pattern, row 1 doesn't need to match anything. The remaining rows match:
|
|||
|
|
row 2 matches row 7, row 3 matches row 6, and row 4 matches row 5.
|
|||
|
|
|
|||
|
|
To summarize your pattern notes, add up the number of columns to the left
|
|||
|
|
of each vertical line of reflection; to that, also add 100 multiplied by
|
|||
|
|
the number of rows above each horizontal line of reflection. In the above
|
|||
|
|
example, the first pattern's vertical line has 5 columns to its left and
|
|||
|
|
the second pattern's horizontal line has 4 rows above it, a total of 405.
|
|||
|
|
|
|||
|
|
Find the line of reflection in each of the patterns in your notes. What
|
|||
|
|
number do you get after summarizing all of your notes?
|
|||
|
|
|
|||
|
|
Your puzzle answer was 27742.
|
|||
|
|
|
|||
|
|
--- Part Two ---
|
|||
|
|
|
|||
|
|
You resume walking through the valley of mirrors and - SMACK! - run
|
|||
|
|
directly into one. Hopefully nobody was watching, because that must have
|
|||
|
|
been pretty embarrassing.
|
|||
|
|
|
|||
|
|
Upon closer inspection, you discover that every mirror has exactly one
|
|||
|
|
smudge: exactly one . or # should be the opposite type.
|
|||
|
|
|
|||
|
|
In each pattern, you'll need to locate and fix the smudge that causes a
|
|||
|
|
different reflection line to be valid. (The old reflection line won't
|
|||
|
|
necessarily continue being valid after the smudge is fixed.)
|
|||
|
|
|
|||
|
|
Here's the above example again:
|
|||
|
|
|
|||
|
|
#.##..##.
|
|||
|
|
..#.##.#.
|
|||
|
|
##......#
|
|||
|
|
##......#
|
|||
|
|
..#.##.#.
|
|||
|
|
..##..##.
|
|||
|
|
#.#.##.#.
|
|||
|
|
|
|||
|
|
#...##..#
|
|||
|
|
#....#..#
|
|||
|
|
..##..###
|
|||
|
|
#####.##.
|
|||
|
|
#####.##.
|
|||
|
|
..##..###
|
|||
|
|
#....#..#
|
|||
|
|
|
|||
|
|
The first pattern's smudge is in the top-left corner. If the top-left #
|
|||
|
|
were instead ., it would have a different, horizontal line of reflection:
|
|||
|
|
|
|||
|
|
1 ..##..##. 1
|
|||
|
|
2 ..#.##.#. 2
|
|||
|
|
3v##......#v3
|
|||
|
|
4^##......#^4
|
|||
|
|
5 ..#.##.#. 5
|
|||
|
|
6 ..##..##. 6
|
|||
|
|
7 #.#.##.#. 7
|
|||
|
|
|
|||
|
|
With the smudge in the top-left corner repaired, a new horizontal line of
|
|||
|
|
reflection between rows 3 and 4 now exists. Row 7 has no corresponding
|
|||
|
|
reflected row and can be ignored, but every other row matches exactly: row
|
|||
|
|
1 matches row 6, row 2 matches row 5, and row 3 matches row 4.
|
|||
|
|
|
|||
|
|
In the second pattern, the smudge can be fixed by changing the fifth
|
|||
|
|
symbol on row 2 from . to #:
|
|||
|
|
|
|||
|
|
1v#...##..#v1
|
|||
|
|
2^#...##..#^2
|
|||
|
|
3 ..##..### 3
|
|||
|
|
4 #####.##. 4
|
|||
|
|
5 #####.##. 5
|
|||
|
|
6 ..##..### 6
|
|||
|
|
7 #....#..# 7
|
|||
|
|
|
|||
|
|
Now, the pattern has a different horizontal line of reflection between
|
|||
|
|
rows 1 and 2.
|
|||
|
|
|
|||
|
|
Summarize your notes as before, but instead use the new different
|
|||
|
|
reflection lines. In this example, the first pattern's new horizontal line
|
|||
|
|
has 3 rows above it and the second pattern's new horizontal line has 1 row
|
|||
|
|
above it, summarizing to the value 400.
|
|||
|
|
|
|||
|
|
In each pattern, fix the smudge and find the different line of reflection.
|
|||
|
|
What number do you get after summarizing the new reflection line in each
|
|||
|
|
pattern in your notes?
|
|||
|
|
|
|||
|
|
Your puzzle answer was 32728.
|
|||
|
|
|
|||
|
|
Both parts of this puzzle are complete! They provide two gold stars: **
|
|||
|
|
|
|||
|
|
At this point, you should [16]return to your Advent calendar and try
|
|||
|
|
another puzzle.
|
|||
|
|
|
|||
|
|
If you still want to see it, you can [17]get your puzzle input.
|
|||
|
|
|
|||
|
|
You can also [Shareon [18]Twitter [19]Mastodon] this puzzle.
|
|||
|
|
|
|||
|
|
References
|
|||
|
|
|
|||
|
|
Visible links
|
|||
|
|
1. https://adventofcode.com/
|
|||
|
|
2. https://adventofcode.com/2023/about
|
|||
|
|
3. https://adventofcode.com/2023/events
|
|||
|
|
4. https://teespring.com/stores/advent-of-code
|
|||
|
|
5. https://adventofcode.com/2023/settings
|
|||
|
|
6. https://adventofcode.com/2023/auth/logout
|
|||
|
|
7. Advent of Code Supporter
|
|||
|
|
https://adventofcode.com/2023/support
|
|||
|
|
8. https://adventofcode.com/2023
|
|||
|
|
9. https://adventofcode.com/2023
|
|||
|
|
10. https://adventofcode.com/2023/support
|
|||
|
|
11. https://adventofcode.com/2023/sponsors
|
|||
|
|
12. https://adventofcode.com/2023/leaderboard
|
|||
|
|
13. https://adventofcode.com/2023/stats
|
|||
|
|
14. https://adventofcode.com/2023/sponsors
|
|||
|
|
15. https://www.janestreet.com/
|
|||
|
|
16. https://adventofcode.com/2023
|
|||
|
|
17. https://adventofcode.com/2023/day/13/input
|
|||
|
|
18. https://twitter.com/intent/tweet?text=I%27ve+completed+%22Point+of+Incidence%22+%2D+Day+13+%2D+Advent+of+Code+2023&url=https%3A%2F%2Fadventofcode%2Ecom%2F2023%2Fday%2F13&related=ericwastl&hashtags=AdventOfCode
|
|||
|
|
19. javascript:void(0);
|