# README
--- 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 .
:
[code]
..X...
.SAMX.
.A..A.
XMAS.S
.X....
[/code]
The actual word search will be full of letters instead. For example:
[code]
MMMSXXMASM
MSAMXMSMSA
AMXSXMAAMM
MSAMASMSMX
XMASAMXAMM
XXAMMXXAMA
SMSMSASXSS
SAXAMASAAA
MAMMMXMMMM
MXMXAXMASX
[/code]
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 .
:
[code]
....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
[/code]
Take a look at the little Elf's word search. How many times doesXMAS
appear?
Your puzzle answer was 2560
.
--- 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:
[code]
M.S
.A.
M.S
[/code]
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-MAS
es have
been kept instead:
[code]
.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.
..........
[/code]
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 anX-MAS
appear?
Your puzzle answer was 1910
.