From 00000190d0e07b5756b366f44f568641d18fcaf7 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Matej=20Jane=C5=BEi=C4=8D?= <janezic.mj@gmail.com>
Date: Tue, 9 Dec 2025 22:05:33 +0100
Subject: [PATCH] feat: add solution 2025/09

---
 data/example/2025/09.txt         |   8 ++
 src/solution/year_2025/day_09.py | 162 +++++++++++++++++++++++++++++++
 2 files changed, 170 insertions(+)
 create mode 100644 data/example/2025/09.txt
 create mode 100644 src/solution/year_2025/day_09.py

diff --git a/data/example/2025/09.txt b/data/example/2025/09.txt
new file mode 100644
index 000000000..c8563ea
--- /dev/null
+++ b/data/example/2025/09.txt
@@ -0,0 +1,8 @@
+7,1
+11,1
+11,7
+9,7
+9,5
+2,5
+2,3
+7,3
diff --git a/src/solution/year_2025/day_09.py b/src/solution/year_2025/day_09.py
new file mode 100644
index 000000000..2a77100
--- /dev/null
+++ b/src/solution/year_2025/day_09.py
@@ -0,0 +1,162 @@
+from collections.abc import Generator
+from typing import Any
+
+Point = tuple[int, int]
+
+
+def _parse_input(input_data) -> list[Point]:
+    points = []
+    for line in input_data.splitlines():
+        a, b = line.split(",")
+        points.append((int(a), int(b)))
+
+    return points
+
+
+def _rectangle_size(p1: Point, p2: Point) -> int:
+    x1, y1 = p1
+    x2, y2 = p2
+
+    return (abs(x1 - x2) + 1) * (abs(y1 - y2) + 1)
+
+
+def part_1(input_data: str) -> Any:
+    lines = _parse_input(input_data)
+
+    m = None
+    for idx, p1 in enumerate(lines):
+        for p2 in lines[idx + 1 :]:
+            size = _rectangle_size(p1, p2)
+            m = max(size, m or size)
+
+    return m
+
+
+def _get_dir(p1: Point, p2: Point) -> Point:
+    x1, y1 = p1
+    x2, y2 = p2
+
+    dx = x2 - x1
+    dy = y2 - y1
+
+    if dx:
+        dx = dx // abs(dx)
+    if dy:
+        dy = dy // abs(dy)
+
+    return dx, dy
+
+
+def _get_segment(p1: Point, p2: Point) -> Generator[Point]:
+    dx, dy = _get_dir(p1, p2)
+
+    points = []
+
+    sx, sy = p1
+    while (sx, sy) != p2:
+        yield sx, sy
+        points.append((sx, sy))
+        sx, sy = sx + dx, sy + dy
+
+    yield p2
+
+
+def _compress_coordinates(points: list[Point], y: bool) -> dict[int, int]:
+    return {v: k for k, v in enumerate(sorted({p[y] for p in points}))}
+
+
+def _find_inner(
+    points: list[Point], xc: dict[int, int], yc: dict[int, int]
+) -> set[Point]:
+    def c(p: Point) -> Point:
+        return xc[p[0]], yc[p[1]]
+
+    inner = set()
+    inside = set()
+
+    for idx in range(len(points)):
+        p1 = points[idx - 1]
+        p2 = points[idx]
+
+        c1, c2 = c(p1), c(p2)
+
+        rng = _get_segment(c1, c2)
+
+        dx, dy = _get_dir(c1, c2)
+        # rotate 90 positive as inside is in the positive direction
+        dx, dy = -dy, dx
+
+        for x, y in rng:
+            inner.add((x, y))
+            inside.add((x + dx, y + dy))
+
+    stack = list(inside - inner)
+
+    dirs = [(0, 1), (0, -1), (1, 0), (-1, 0)]
+    while stack:
+        px, py = stack.pop()
+        inner.add((px, py))
+
+        for dx, dy in dirs:
+            nx, ny = px + dx, py + dy
+            if (nx, ny) in inner:
+                continue
+            stack.append((nx, ny))
+
+    return inner
+
+
+def _get_corner_points(p1: Point, p2: Point) -> tuple[Point, ...]:
+    if p1 == p2:
+        return (p1,)
+
+    px1, py1 = p1
+    px2, py2 = p2
+    p3 = px1, py2
+    p4 = px2, py1
+
+    return p1, p3, p2, p4
+
+
+def part_2(input_data: str) -> Any:
+    points = _parse_input(input_data)
+
+    x_compression = _compress_coordinates(points, False)
+    y_compression = _compress_coordinates(points, True)
+
+    def c(p: Point) -> Point:
+        return x_compression[p[0]], y_compression[p[1]]
+
+    inner = _find_inner(points, x_compression, y_compression)
+
+    m = None
+
+    for idx, p1 in enumerate(points):
+        c1 = c(p1)
+        for p2 in points[idx + 1 :]:
+            c2 = c(p2)
+
+            c1, c2, c3, c4 = _get_corner_points(c1, c2)
+
+            is_inside = (
+                all(x in inner for x in _get_segment(c1, c2))
+                and all(x in inner for x in _get_segment(c2, c3))
+                and all(x in inner for x in _get_segment(c3, c4))
+                and all(x in inner for x in _get_segment(c4, c1))
+            )
+
+            if not is_inside:
+                continue
+
+            size = _rectangle_size(p1, p2)
+            m = max(m or size, size)
+
+    return m
+
+
+def test_part_1(example_data):
+    assert part_1(example_data) == 50
+
+
+def test_part_2(example_data):
+    assert part_2(example_data) == 24