2025: improve folder names

2024/04/README.md

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+# Day 4: Ceres Search
+
+[https://adventofcode.com/2024/day/4](https://adventofcode.com/2024/day/4)
+
+## Description
+
+### Part One
+
+"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](https://adventofcode.com/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?_
+
+### 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 <span title="This part originally involved searching for something else, but this joke was too dumb to pass up."><code><em>X-MAS</em></code></span> 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?_