From dee3d1832176a0caa60770e87ff668811c1ebd8e Mon Sep 17 00:00:00 2001
From: Tomasz Kramkowski <tk@the-tk.com>
Date: Mon, 13 Dec 2021 10:12:10 +0000
Subject: day 13

---
 12.py |  6 +++---
 13.py | 41 +++++++++++++++++++++++++++++++++++++++++
 2 files changed, 44 insertions(+), 3 deletions(-)
 create mode 100644 13.py

diff --git a/12.py b/12.py
index f471e07..c46fbe6 100644
--- a/12.py
+++ b/12.py
@@ -10,7 +10,7 @@ with open_day(12) as f:
         adj[a].add(b)
         adj[b].add(a)
 
-def count_paths(look_twice=False):
+def count_paths(adj, look_twice=False):
     @cache
     def f(node, seen, saw_once=None):
         def descend(node, seen, saw_once):
@@ -27,5 +27,5 @@ def count_paths(look_twice=False):
         return total + descend(node, seen, saw_once)
     return sum(f(n, frozenset(('start',))) for n in adj['start'])
 
-print(count_paths())
-print(count_paths(True))
+print(count_paths(adj))
+print(count_paths(adj, True))
diff --git a/13.py b/13.py
new file mode 100644
index 0000000..4003f9c
--- /dev/null
+++ b/13.py
@@ -0,0 +1,41 @@
+from utils import open_day
+from dataclasses import dataclass
+
+@dataclass
+class Point:
+    x: int
+    y: int
+    @staticmethod
+    def from_str(s: str) -> 'Point':
+        return Point(*map(int, s.split(',', maxsplit=1)))
+
+@dataclass
+class Fold:
+    axis: str
+    pos: int
+    @staticmethod
+    def from_str(s: str) -> 'Fold':
+        axis, pos = s.split(' ')[2].split('=', maxsplit=1)
+        return Fold(axis, int(pos))
+
+with open_day(13) as f:
+    parts = f.read().rstrip().split('\n\n')
+    points = [Point.from_str(l) for l in parts[0].split('\n')]
+    folds = [Fold.from_str(l) for l in parts[1].split('\n')]
+
+def fold(points: list[Point], fold: Fold):
+    for i in range(len(points)):
+        point_pos = getattr(points[i], fold.axis)
+        if point_pos > fold.pos:
+            setattr(points[i], fold.axis, 2 * fold.pos - point_pos)
+
+for i, f in enumerate(folds):
+    fold(points, f)
+    if i == 0: print(len(set((p.x, p.y) for p in points)))
+maxx = min(f.pos for f in folds if f.axis == 'x')
+maxy = min(f.pos for f in folds if f.axis == 'y')
+points = set((p.x, p.y) for p in points)
+for y in range(maxy):
+    for x in range(maxx):
+        print('#' if (x, y) in points else '.', end='')
+    print()
-- 
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