Description
XMASXMASXMASXMAS XMASXMASXMASXMAS XMASXMASXMASXMAS XMASXMASXMASXMAS XMASXMASXMASXMAS XMASXMASXMASXMAS XMASXMASXMASXMAS XMASXMASXMASXMAS
"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?
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?
Notes
- Part I: Gone from 1D -> 2D
- My first thought is to break down the puzzle by each line horizontally and then vertically, checking for forward and backwards instances of 'XMAS'. Getting the diagonals will be a little dicier, but I think doable.
- Needed SO for a way to get the diagonals from a 2D array
- First submission was too high. Re-checked code and realized I forgot to add a flag to check for the reverse of a diagonal. Got it!
- Part II: no regex needed! Improved my Ruby Grid class and used it to build a double loop checking for 'A' and then if its NW, NE, SW, and SE neighbors matched the right attributes. Easier than Part I for me.