From 5a9667094c61a24cdbb92e6ec581b43ce6ac2fc2 Mon Sep 17 00:00:00 2001
From: Bert Peters <bert@bertptrs.nl>
Date: Mon, 2 Dec 2024 08:54:30 +0100
Subject: [PATCH] Implement 2024 day 2

---
 2024/src/aoc/days/day2.py | 47 +++++++++++++++++++++++++++++++++++++++
 2024/tests/samples/02.txt |  6 +++++
 2024/tests/test_day2.py   | 26 ++++++++++++++++++++++
 3 files changed, 79 insertions(+)
 create mode 100644 2024/src/aoc/days/day2.py
 create mode 100644 2024/tests/samples/02.txt
 create mode 100644 2024/tests/test_day2.py

diff --git a/2024/src/aoc/days/day2.py b/2024/src/aoc/days/day2.py
new file mode 100644
index 0000000..e303eb1
--- /dev/null
+++ b/2024/src/aoc/days/day2.py
@@ -0,0 +1,47 @@
+import numpy
+
+from . import SeparateRunner
+
+
+def _safe(nums: numpy.ndarray) -> bool:
+    steps = nums[1:] - nums[:-1]
+
+    if numpy.all(steps > 0):
+        return numpy.all((steps >= 1) & (steps <= 3))
+    elif numpy.all(steps < 0):
+        return numpy.all((steps <= -1) & (steps >= -3))
+    else:
+        return False
+
+
+def is_safe(line: str) -> bool:
+    nums = numpy.fromstring(line, dtype=numpy.int32, sep=" ")
+
+    return _safe(nums)
+
+
+def is_savable(line: str) -> bool:
+    nums = numpy.fromstring(line, dtype=numpy.int32, sep=" ")
+
+    return any(
+        _safe(numpy.concatenate((nums[:i], nums[i + 1 :]), axis=None))
+        for i in range(len(nums))
+    )
+
+
+class DayRunner(SeparateRunner):
+    @classmethod
+    def part1(cls, data: str) -> int:
+        lines = data.strip().split("\n")
+
+        safe = sum(1 for line in lines if is_safe(line))
+
+        return safe
+
+    @classmethod
+    def part2(cls, data: str) -> int:
+        lines = data.strip().split("\n")
+
+        safe = sum(1 for line in lines if is_savable(line))
+
+        return safe
diff --git a/2024/tests/samples/02.txt b/2024/tests/samples/02.txt
new file mode 100644
index 0000000..b49c10d
--- /dev/null
+++ b/2024/tests/samples/02.txt
@@ -0,0 +1,6 @@
+7 6 4 2 1
+1 2 7 8 9
+9 7 6 2 1
+1 3 2 4 5
+8 6 4 4 1
+1 3 6 7 9
diff --git a/2024/tests/test_day2.py b/2024/tests/test_day2.py
new file mode 100644
index 0000000..f9843b1
--- /dev/null
+++ b/2024/tests/test_day2.py
@@ -0,0 +1,26 @@
+import os
+
+from aoc.days.day2 import DayRunner, is_savable
+
+
+def get_data() -> str:
+    sample = os.path.dirname(__file__) + "/samples/02.txt"
+    with open(sample, mode="rt", encoding="utf-8") as f:
+        return f.read()
+
+
+def test_individual_samples() -> None:
+    assert is_savable("7 6 4 2 1")
+    assert not is_savable("1 2 7 8 9")
+    assert not is_savable("9 7 6 2 1")
+    assert is_savable("1 3 2 4 5")
+    assert is_savable("8 6 4 4 1")
+    assert is_savable("1 3 6 7 9")
+
+
+def test_sample_part1() -> None:
+    assert DayRunner.part1(get_data()) == 2
+
+
+def test_sample_part2() -> None:
+    assert DayRunner.part2(get_data()) == 4