From 4cb37bc59b695192ffc95fd686bea05e1bd931ab Mon Sep 17 00:00:00 2001
From: Tomasz Kramkowski <tomasz@kramkow.ski>
Date: Sun, 10 Dec 2023 13:05:33 +0000
Subject: day 10 jank

---
 10.py | 118 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 118 insertions(+)
 create mode 100644 10.py

diff --git a/10.py b/10.py
new file mode 100644
index 0000000..a024909
--- /dev/null
+++ b/10.py
@@ -0,0 +1,118 @@
+import re
+from collections.abc import Iterator
+from dataclasses import dataclass
+from sys import stdin
+from typing import Self
+
+
+@dataclass(frozen=True, slots=True, order=True)
+class Point:
+    x: int
+    y: int
+
+    def __sub__(self, other: Self) -> Self:
+        return self.__class__(self.x - other.x, self.y - other.y)
+
+    def __add__(self, other: Self) -> Self:
+        return self.__class__(self.x + other.x, self.y + other.y)
+
+    def __neg__(self) -> Self:
+        return self.__class__(-self.x, -self.y)
+
+
+def next_pos(current: Point, prev: Point, pipe: str) -> Point:
+    mapping = {
+        Point(0, 1): {  # from north \/
+            "|": Point(0, 1),  # to south \/
+            "L": Point(1, 0),  # to east ->
+            "J": Point(-1, 0),  # to west <-
+        },
+        Point(-1, 0): {  # from east <-
+            "-": Point(-1, 0),  # to west <-
+            "F": Point(0, 1),  # to south \/
+            "L": Point(0, -1),  # to north /\
+        },
+        Point(0, -1): {  # from south /\
+            "|": Point(0, -1),  # to north /\
+            "F": Point(1, 0),  # to east ->
+            "7": Point(-1, 0),  # to west <-
+        },
+        Point(1, 0): {  # from west ->
+            "-": Point(1, 0),  # to east ->
+            "7": Point(0, 1),  # to south \/
+            "J": Point(0, -1),  # to north /\
+        },
+    }
+    return current + mapping[current - prev][pipe]
+
+
+def neighbours(point: Point) -> Iterator[Point]:
+    for d in (Point(0, -1), Point(1, 0), Point(0, 1), Point(-1, 0)):
+        yield point + d
+
+
+inp = [line.rstrip() for line in stdin]
+
+start = next(
+    Point(x, y) for y, l in enumerate(inp) for x, c in enumerate(l) if c == "S"
+)
+
+prev = start
+if inp[start.y - 1][start.x] in {"|", "F", "7"}:
+    current = start + Point(0, -1)
+elif inp[start.y][start.x + 1] in {"-", "J", "7"}:
+    current = start + Point(1, 0)
+elif inp[start.y + 1][start.x] in {"|", "J", "L"}:
+    current = start + Point(0, 1)
+elif inp[start.y][start.x - 1] in {"-", "L", "F"}:
+    current = start + Point(-1, 0)
+else:
+    raise ValueError
+
+first_after_start = current
+last_before_start = current
+
+bounds: set[Point] = set((start,))
+length = 1
+while inp[current.y][current.x] != "S":
+    bounds.add(current)
+    current, prev = next_pos(current, prev, inp[current.y][current.x]), current
+    last_before_start = prev
+    length += 1
+
+print(length // 2)
+
+dirs = list(sorted((start - first_after_start, start - last_before_start)))
+
+start_replacement = {
+    "S": {
+        (Point(-1, 0), Point(0, -1)): "F",  # ES
+        (Point(-1, 0), Point(0, 1)): "L",  # EN
+        (Point(-1, 0), Point(1, 0)): "-",  # EW
+        (Point(0, -1), Point(0, 1)): "|",  # SN
+        (Point(0, -1), Point(1, 0)): "7",  # SW
+        (Point(0, 1), Point(1, 0)): "J",  # NW
+    }[(dirs[0], dirs[1])]
+}
+
+
+inp2 = [
+    "".join(
+        start_replacement.get(c, c) if Point(x, y) in bounds else "."
+        for x, c in enumerate(line)
+    )
+    for y, line in enumerate(inp)
+]
+
+for pattern, repl in (("L-*J", ""), ("L-*7", "|"), ("F-*J", "|"), ("F-*7", "")):
+    inp2 = [re.sub(pattern, repl, l) for l in inp2]
+
+inner = 0
+for line in inp2:
+    outside = True
+    for c in line:
+        if c == "|":
+            outside = not outside
+        elif c == "." and not outside:
+            inner += 1
+print(inner)
-- 
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