feat(2024): day 4 - Ceres Search 🕵️‍♂️

2024/Day04/README.md

@@ -1,3 +1,86 @@
-# --- Day 0: Template ---
+# --- Day 4: Ceres Search ---
 
-To be used as template for the other days.
+"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 `2662`.
+
+## --- 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 `2034`.
+
+Both parts of this puzzle are complete! They provide two gold stars: `**`

2024/Day04/ceres_search.py

@@ -0,0 +1,53 @@
+from utils.directions import ALL_DIRECTIONS
+
+
+class CeresSearch:
+    TARGET_WORD = "XMAS"
+
+    def __init__(self, lines: list[str]):
+        self.lines = lines
+        self.rows = len(lines)
+        self.cols = len(lines[0]) if lines else 0
+
+    def dfs(self, x: int, y: int, idx: int, direction: tuple[int, int]) -> int:
+        if not (0 <= x < self.rows and 0 <= y < self.cols):
+            return 0
+        if self.lines[x][y] != self.TARGET_WORD[idx]:
+            return 0
+        if idx == len(self.TARGET_WORD) - 1:
+            return 1
+
+        dx, dy = direction
+        return self.dfs(x + dx, y + dy, idx + 1, direction)
+
+    def search_xmas(self) -> int:
+        count = 0
+        for i in range(self.rows):
+            for j in range(self.cols):
+                if self.lines[i][j] == self.TARGET_WORD[0]:
+                    for direction in ALL_DIRECTIONS:
+                        count += self.dfs(i, j, 0, direction)
+
+        return count
+
+    def is_x_mas(self, x: int, y: int) -> bool:
+        corners = [
+            self.lines[x - 1][y - 1],
+            self.lines[x - 1][y + 1],
+            self.lines[x + 1][y - 1],
+            self.lines[x + 1][y + 1],
+        ]
+        return corners in [
+            ["M", "S", "M", "S"],
+            ["S", "M", "S", "M"],
+            ["M", "M", "S", "S"],
+            ["S", "S", "M", "M"],
+        ]
+
+    def search_x_mas_patterns(self) -> int:
+        return sum(
+            1
+            for i in range(1, self.rows - 1)
+            for j in range(1, self.cols - 1)
+            if self.lines[i][j] == "A" and self.is_x_mas(i, j)
+        )