From 0ce095e9e5bb679b628ee7e40b32ebf0fd61194f Mon Sep 17 00:00:00 2001
From: Bert Peters <bert@bertptrs.nl>
Date: Wed, 4 Dec 2024 12:27:06 +0100
Subject: [PATCH] Implement 2024 day 4

---
 2024/src/aoc/days/day4.py   | 69 +++++++++++++++++++++++++++++++++++++
 2024/tests/__init__.py      |  0
 2024/tests/samples/04.1.txt |  5 +++
 2024/tests/samples/04.2.txt | 10 ++++++
 2024/tests/test_day4.py     | 26 ++++++++++++++
 5 files changed, 110 insertions(+)
 create mode 100644 2024/src/aoc/days/day4.py
 create mode 100644 2024/tests/__init__.py
 create mode 100644 2024/tests/samples/04.1.txt
 create mode 100644 2024/tests/samples/04.2.txt
 create mode 100644 2024/tests/test_day4.py

diff --git a/2024/src/aoc/days/day4.py b/2024/src/aoc/days/day4.py
new file mode 100644
index 0000000..87f8f00
--- /dev/null
+++ b/2024/src/aoc/days/day4.py
@@ -0,0 +1,69 @@
+import numpy
+
+from . import SeparateRunner
+
+
+class DayRunner(SeparateRunner):
+    @classmethod
+    def part1(cls, input: str) -> int:
+        grid = numpy.array(list(map(list, input.strip().split("\n"))))
+
+        found = 0
+
+        directions = [
+            (-1, -1),
+            (-1, 0),
+            (-1, 1),
+            (0, -1),
+            (0, 1),
+            (1, -1),
+            (1, 0),
+            (1, 1),
+        ]
+
+        word = "XMAS"
+
+        for y in range(grid.shape[0]):
+            for x in range(grid.shape[1]):
+                if grid[y, x] != "X":
+                    continue
+
+                for dx, dy in directions:
+                    end_x = x + 3 * dx
+                    end_y = y + 3 * dy
+
+                    if (
+                        end_x < 0
+                        or end_x >= grid.shape[1]
+                        or end_y < 0
+                        or end_y >= grid.shape[0]
+                    ):
+                        continue
+
+                    if all(
+                        grid[y + i * dy, x + i * dx] == c for i, c in enumerate(word)
+                    ):
+                        found += 1
+
+        return found
+
+    @classmethod
+    def part2(cls, input: str) -> int:
+        grid = numpy.array(list(map(list, input.strip().split("\n"))))
+
+        found = 0
+
+        magic = ord("M") ^ ord("S")
+
+        for y in range(1, grid.shape[0] - 1):
+            for x in range(1, grid.shape[1] - 1):
+                if grid[y, x] != "A":
+                    continue
+
+                first_diag = ord(grid[y - 1, x - 1]) ^ ord(grid[y + 1, x + 1])
+                secnd_diag = ord(grid[y - 1, x + 1]) ^ ord(grid[y + 1, x - 1])
+
+                if first_diag == magic and secnd_diag == magic:
+                    found += 1
+
+        return found
diff --git a/2024/tests/__init__.py b/2024/tests/__init__.py
new file mode 100644
index 0000000..e69de29
diff --git a/2024/tests/samples/04.1.txt b/2024/tests/samples/04.1.txt
new file mode 100644
index 0000000..06d2c4e
--- /dev/null
+++ b/2024/tests/samples/04.1.txt
@@ -0,0 +1,5 @@
+..X...
+.SAMX.
+.A..A.
+XMAS.S
+.X....
diff --git a/2024/tests/samples/04.2.txt b/2024/tests/samples/04.2.txt
new file mode 100644
index 0000000..1f4eda2
--- /dev/null
+++ b/2024/tests/samples/04.2.txt
@@ -0,0 +1,10 @@
+MMMSXXMASM
+MSAMXMSMSA
+AMXSXMAAMM
+MSAMASMSMX
+XMASAMXAMM
+XXAMMXXAMA
+SMSMSASXSS
+SAXAMASAAA
+MAMMMXMMMM
+MXMXAXMASX
diff --git a/2024/tests/test_day4.py b/2024/tests/test_day4.py
new file mode 100644
index 0000000..7ff7887
--- /dev/null
+++ b/2024/tests/test_day4.py
@@ -0,0 +1,26 @@
+import os
+
+import pytest
+
+from aoc.days.day4 import DayRunner
+
+
+def get_data(which: int) -> str:
+    sample = os.path.dirname(__file__) + f"/samples/04.{which}.txt"
+    with open(sample, mode="rt", encoding="utf-8") as f:
+        return f.read()
+
+
+@pytest.mark.parametrize(
+    "input,answer",
+    [
+        (get_data(1), 4),
+        (get_data(2), 18),
+    ],
+)
+def test_sample_part1(input: str, answer: int) -> None:
+    assert DayRunner.part1(input) == answer
+
+
+def test_sample_part2() -> None:
+    assert DayRunner.part2(get_data(2)) == 9