2024 day 4 part 1 and 2

README.md

@@ -15,7 +15,7 @@
 - 2021 - ★★★★★ ★★★★★ ★★★★★ ★★★
 - 2022 - ★★★★★ ★★★★★ ★★★★★ ★☆
 - 2023 - ★★★★★ ★★★★★ ★★★★★ ★★★☆
-- 2024 - ★★★
+- 2024 - ★★★★
 
 ## How to use
 

src/year2024/day04a.py

@@ -0,0 +1,53 @@
+"""2024 - Day 4 Part 1: Ceres Search"""
+
+SHIFTS = {
+    # dr  dc
+    (-1, -1),
+    (-1, 0),
+    (-1, +1),
+    (0, +1),
+    (+1, +1),
+    (+1, 0),
+    (+1, -1),
+    (0, -1),
+}
+
+XMAS = "XMAS"
+
+
+def is_xmas(r: int, c: int, data: list[str]) -> int:
+    count = 0
+
+    rows = len(data)
+    cols = len(data[0])
+
+    for dr, dc in SHIFTS:
+        nr = r
+        nc = c
+
+        for i in range(4):
+            in_bounds = 0 <= nr < rows and 0 <= nc < cols
+            if not in_bounds or XMAS[i] != data[nr][nc]:
+                break
+
+            nr += dr
+            nc += dc
+        else:
+            count += 1
+
+    return count
+
+
+def solve(task: str) -> int:
+    data = task.split("\n")
+
+    ans = 0
+
+    rows = len(data)
+    cols = len(data[0])
+
+    for r in range(rows):
+        for c in range(cols):
+            ans += is_xmas(r, c, data)
+
+    return ans

src/year2024/day04b.py

@@ -0,0 +1,42 @@
+"""2024 - Day 4 Part 2: Ceres Search"""
+
+OPTIONS = {
+    "MM" "A" "SS",
+    "MS" "A" "MS",
+    "SS" "A" "MM",
+    "SM" "A" "SM",
+}
+
+SHIFTS = (
+    # dr dc
+    (0, 0),
+    (0, +2),
+    (+1, +1),
+    (+2, 0),
+    (+2, +2),
+)
+
+
+def is_xmas(r: int, c: int, data: list[str]) -> bool:
+    start = data[r][c]
+
+    if start not in {"S", "M"}:
+        return False
+
+    word = "".join(data[r + dr][c + dc] for dr, dc in SHIFTS)
+    return word in OPTIONS
+
+
+def solve(task: str) -> int:
+    data = task.split("\n")
+
+    ans = 0
+
+    rows = len(data)
+    cols = len(data[0])
+
+    for r in range(rows - 2):
+        for c in range(cols - 2):
+            ans += is_xmas(r, c, data)
+
+    return ans

tests/src/year2024/test_day04a.py

@@ -0,0 +1,23 @@
+"""2024 - Day 4 Part 1: Ceres Search"""
+
+from textwrap import dedent
+
+from src.year2024.day04a import solve
+
+
+def test_solve():
+    task = dedent(
+        """
+        MMMSXXMASM
+        MSAMXMSMSA
+        AMXSXMAAMM
+        MSAMASMSMX
+        XMASAMXAMM
+        XXAMMXXAMA
+        SMSMSASXSS
+        SAXAMASAAA
+        MAMMMXMMMM
+        MXMXAXMASX
+        """
+    ).strip()
+    assert solve(task) == 18

tests/src/year2024/test_day04b.py

@@ -0,0 +1,23 @@
+"""2024 - Day 4 Part 2: Ceres Search"""
+
+from textwrap import dedent
+
+from src.year2024.day04b import solve
+
+
+def test_solve():
+    task = dedent(
+        """
+        .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.
+        ..........
+        """
+    ).strip()
+    assert solve(task) == 9