2.7 KiB
--- Day 4: Ceres Search ---
"Looks like the Chief's not here. Next!" One of The Historians pulls out a device and pushes the only button on it. After a brief flash, you recognize the interior of the Ceres monitoring station!
As the search for the Chief continues, a small Elf who lives on the
station tugs on your shirt; she'd like to know if you could help her
with her word search (your puzzle input). She only has to find one
word: XMAS.
This word search allows words to be horizontal, vertical, diagonal,
written backwards, or even overlapping other words. It's a little
unusual, though, as you don't merely need to find one instance of
XMAS - you need to find all of them. Here are a few ways XMAS
might appear, where irrelevant characters have been replaced with .:
..X...
.SAMX.
.A..A.
XMAS.S
.X....
The actual word search will be full of letters instead. For example:
MMMSXXMASM
MSAMXMSMSA
AMXSXMAAMM
MSAMASMSMX
XMASAMXAMM
XXAMMXXAMA
SMSMSASXSS
SAXAMASAAA
MAMMMXMMMM
MXMXAXMASX
In this word search, XMAS occurs a total of 18 times; here's the
same word search again, but where letters not involved in any XMAS
have been replaced with .:
....XXMAS.
.SAMXMS...
...S..A...
..A.A.MS.X
XMASAMX.MM
X.....XA.A
S.S.S.S.SS
.A.A.A.A.A
..M.M.M.MM
.X.X.XMASX
Take a look at the little Elf's word search. How many times does
XMAS appear?
Your puzzle answer was 2378.
--- Part Two ---
The Elf looks quizzically at you. Did you misunderstand the assignment?
Looking for the instructions, you flip over the word search to find that
this isn't actually an XMAS puzzle; it's an
X-MAS
puzzle in which you're supposed to find two MAS in the shape of an
X. One way to achieve that is like this:
M.S
.A.
M.S
Irrelevant characters have again been replaced with . in the above
diagram. Within the X, each MAS can be written forwards or
backwards.
Here's the same example from before, but this time all of the X-MASes
have been kept instead:
.M.S......
..A..MSMS.
.M.S.MAA..
..A.ASMSM.
.M.S.M....
..........
S.S.S.S.S.
.A.A.A.A..
M.M.M.M.M.
..........
In this example, an X-MAS appears 9 times.
Flip the word search from the instructions back over to the word search
side and try again. How many times does an X-MAS appear?
Your puzzle answer was 1796.
Both parts of this puzzle are complete! They provide two gold stars: **
At this point, you should return to your Advent calendar and try another puzzle.
If you still want to see it, you can get your puzzle input.