From a1db2a4adfc72b76548db83395adcbdd8189ffd2 Mon Sep 17 00:00:00 2001
From: Nettika <git@nettika.cat>
Date: Mon, 2 Dec 2024 00:43:39 -0800
Subject: [PATCH] Implement day 2 solver

---
 puzzles/2.py   | 62 ++++++++++++++++++++++++++++++++++++++++++++++++++
 pyproject.toml |  2 +-
 2 files changed, 63 insertions(+), 1 deletion(-)
 create mode 100644 puzzles/2.py

diff --git a/puzzles/2.py b/puzzles/2.py
new file mode 100644
index 0000000..4bff707
--- /dev/null
+++ b/puzzles/2.py
@@ -0,0 +1,62 @@
+from itertools import islice
+from typing import Iterator
+from more_itertools import ilen
+
+test_input = """
+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
+""".strip()
+
+test_solution_p1 = 2
+test_solution_p2 = 4
+
+
+def solve_p1(puzzle_input: str) -> int:
+    reports = _parse_reports(puzzle_input)
+    delta_reports = (_deltas(report) for report in reports)
+    safe_delta_reports = filter(_is_gradual_monotonic, delta_reports)
+    return ilen(safe_delta_reports)
+
+
+def solve_p2(puzzle_input: str) -> int:
+    reports = _parse_reports(puzzle_input)
+    dampened_report_collections = (_dampen_permutations(report) for report in reports)
+    delta_report_collections = (
+        (_deltas(report) for report in report_collection)
+        for report_collection in dampened_report_collections
+    )
+    safe_report_collections = filter(
+        lambda delta_report_collection: any(
+            _is_gradual_monotonic(delta_report)
+            for delta_report in delta_report_collection
+        ),
+        delta_report_collections,
+    )
+    return ilen(safe_report_collections)
+
+
+def _parse_reports(puzzle_input: str) -> Iterator[tuple[int, ...]]:
+    lines = puzzle_input.splitlines()
+    return (tuple(int(level) for level in line.split(" ")) for line in lines)
+
+
+def _deltas(report: tuple[int, ...]) -> tuple[int, ...]:
+    pairs = zip(report, islice(report, 1, None))
+    return tuple(b - a for a, b in pairs)
+
+
+def _is_gradual_monotonic(delta_report: tuple[int]) -> bool:
+    sign = 1 if delta_report[0] > 0 else -1
+    return all(
+        delta != 0 and delta / abs(delta) == sign and abs(delta) < 4
+        for delta in delta_report
+    )
+
+
+def _dampen_permutations(report: tuple[int, ...]) -> Iterator[tuple[int, ...]]:
+    yield report
+    yield from (report[:i] + report[i + 1 :] for i in range(0, len(report)))
diff --git a/pyproject.toml b/pyproject.toml
index 143b244..91a43bd 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -2,4 +2,4 @@
 name = "advent-of-code-2024"
 version = "0.0.0"
 description = "Advent of Code 2024"
-dependencies = ["advent"]
+dependencies = ["advent", "more-itertools"]