From 0c7c54b5c964f78234b828b861f32beff057833f Mon Sep 17 00:00:00 2001
From: Bert Peters <bert@bertptrs.nl>
Date: Fri, 6 Dec 2024 09:20:08 +0100
Subject: [PATCH] Implement 2024 day 6

---
 2024/src/aoc/days/day6.py | 105 ++++++++++++++++++++++++++++++++++++++
 2024/tests/samples/06.txt |  10 ++++
 2024/tests/test_day6.py   |  17 ++++++
 3 files changed, 132 insertions(+)
 create mode 100644 2024/src/aoc/days/day6.py
 create mode 100644 2024/tests/samples/06.txt
 create mode 100644 2024/tests/test_day6.py

diff --git a/2024/src/aoc/days/day6.py b/2024/src/aoc/days/day6.py
new file mode 100644
index 0000000..b327383
--- /dev/null
+++ b/2024/src/aoc/days/day6.py
@@ -0,0 +1,105 @@
+import numpy
+
+from . import SeparateRunner
+
+
+def does_loop(
+    grid: numpy.array,
+    x: int,
+    y: int,
+    dx: int,
+    dy: int,
+    visited: set[tuple[int, int, int, int]],
+) -> bool:
+    try:
+        while True:
+            while y + dy >= 0 and x + dx >= 0 and grid[y + dy, x + dx] == "#":
+                dx, dy = -dy, dx
+
+            x += dx
+            y += dy
+
+            if x < 0 or y < 0:
+                return False
+
+            pos = (x, y, dx, dy)
+
+            if pos in visited:
+                return True
+            else:
+                visited.add(pos)
+    except IndexError:
+        return False
+
+
+class DayRunner(SeparateRunner):
+    @classmethod
+    def part1(cls, input: str) -> int:
+        grid = input.strip().split("\n")
+
+        for y, line in enumerate(grid):
+            if (x := line.find("^")) != -1:
+                break
+
+        dx = 0
+        dy = -1
+
+        visited = {(x, y)}
+
+        try:
+            while True:
+                nx = x + dx
+                ny = y + dy
+
+                if grid[ny][nx] == "#":
+                    dx, dy = -dy, dx
+                else:
+                    x, y = nx, ny
+                    visited.add((x, y))
+        except IndexError:
+            pass
+
+        return len(visited)
+
+    @classmethod
+    def part2(cls, input: str) -> int:
+        grid = numpy.array(list(map(list, input.strip().split("\n"))))
+        y, x = numpy.where(grid == "^")
+
+        y = y[0]
+        x = x[0]
+
+        dx = 0
+        dy = -1
+        loops = 0
+
+        visited = {(x, y, dx, dy)}
+        tiles_visited = {(x, y)}
+
+        try:
+            while True:
+                while y + dy >= 0 and x + dx >= 0 and grid[y + dy, x + dx] == "#":
+                    dx, dy = -dy, dx
+
+                nx = x + dx
+                ny = y + dy
+
+                if nx < 0 or ny < 0:
+                    break
+
+                if (nx, ny) not in tiles_visited:
+                    # check for a loop
+                    grid[ny, nx] = "#"
+                    if does_loop(grid, x, y, dx, dy, visited.copy()):
+                        loops += 1
+                        grid[ny, nx] = "L"
+                    else:
+                        grid[ny, nx] = "."
+
+                x, y = nx, ny
+                tiles_visited.add((x, y))
+                visited.add((x, y, dx, dy))
+        except IndexError:
+            pass
+
+        return loops
diff --git a/2024/tests/samples/06.txt b/2024/tests/samples/06.txt
new file mode 100644
index 0000000..a4eb402
--- /dev/null
+++ b/2024/tests/samples/06.txt
@@ -0,0 +1,10 @@
+....#.....
+.........#
+..........
+..#.......
+.......#..
+..........
+.#..^.....
+........#.
+#.........
+......#...
diff --git a/2024/tests/test_day6.py b/2024/tests/test_day6.py
new file mode 100644
index 0000000..3245015
--- /dev/null
+++ b/2024/tests/test_day6.py
@@ -0,0 +1,17 @@
+import os
+
+from aoc.days.day6 import DayRunner
+
+
+def get_data() -> str:
+    sample = os.path.dirname(__file__) + "/samples/06.txt"
+    with open(sample, mode="rt", encoding="utf-8") as f:
+        return f.read()
+
+
+def test_sample_part1() -> None:
+    assert DayRunner.part1(get_data()) == 41
+
+
+def test_sample_part2() -> None:
+    assert DayRunner.part2(get_data()) == 6