Add 2024 Day 04

2024-12-04 18:56:08 +01:00 · 2024-12-04 18:56:08 +01:00 · 4675717cea
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+"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](/2019/day/10)!
+
+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 `2530`.
+
+\--- 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-MAS`es 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 `1921`.
+
+Both parts of this puzzle are complete! They provide two gold stars: \*\*
+
+At this point, you should [return to your Advent calendar](/2024) and try another puzzle.
+
+If you still want to see it, you can [get your puzzle input](4/input).