From cb5b2b97e0638d2e346124787d37efe5e24a9e19 Mon Sep 17 00:00:00 2001
From: Holly McFarland <me@hollymcfarland.com>
Date: Sat, 6 Dec 2025 15:12:44 -0500
Subject: [PATCH] day 4

---
 day-04/part-1.py | 52 +++++++++++++++++++++++++++++++++++++++++++
 day-04/part-2.py | 57 ++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 109 insertions(+)
 create mode 100644 day-04/part-1.py
 create mode 100644 day-04/part-2.py

diff --git a/day-04/part-1.py b/day-04/part-1.py
new file mode 100644
index 0000000..6d27b66
--- /dev/null
+++ b/day-04/part-1.py
@@ -0,0 +1,52 @@
+import aocd
+
+from enum import Enum
+
+class Direction(complex, Enum):
+    NORTH = -1j
+    SOUTH = 1j
+    EAST = -1
+    WEST = 1
+    NORTHWEST = NORTH+WEST
+    NORTHEAST = NORTH+EAST
+    SOUTHWEST = SOUTH+WEST
+    SOUTHEAST = SOUTH+EAST
+
+class Paper:
+    def __init__(self, x, y, floor):
+        self.coords = complex(real=x, imag=y)
+        self.floor = floor
+    
+    @property
+    def x(self):
+        return int(self.coords.real)
+    
+    @property
+    def y(self):
+        return int(self.coords.imag)
+    
+    @property
+    def neighbours(self):
+        yield from filter(None, (self.floor.get(self.coords + dir) for dir in Direction))
+
+def parse(data):
+    floor = {}
+
+    for y, line in enumerate(data.split('\n')):
+        for x, char in enumerate(line):
+            if char == '@':
+                floor[complex(real=x, imag=y)] = Paper(x, y, floor)
+    
+    return floor
+
+def is_accessible(paper):
+    return sum(1 for _ in paper.neighbours) < 4
+
+def main(data):
+    floor = parse(data.strip())
+    return sum(is_accessible(paper) for paper in floor.values())
+
+if __name__ == '__main__':
+    solution = main(aocd.get_data(day=4, year=2025))
+    print(solution)
+    aocd.submit(solution, part='a', day=4, year=2025)
\ No newline at end of file
diff --git a/day-04/part-2.py b/day-04/part-2.py
new file mode 100644
index 0000000..105cfc1
--- /dev/null
+++ b/day-04/part-2.py
@@ -0,0 +1,57 @@
+import aocd
+
+from enum import Enum
+
+class Direction(complex, Enum):
+    NORTH = -1j
+    SOUTH = 1j
+    EAST = -1
+    WEST = 1
+    NORTHWEST = NORTH+WEST
+    NORTHEAST = NORTH+EAST
+    SOUTHWEST = SOUTH+WEST
+    SOUTHEAST = SOUTH+EAST
+
+class Paper:
+    def __init__(self, x, y, floor):
+        self.coords = complex(real=x, imag=y)
+        self.floor = floor
+    
+    @property
+    def x(self):
+        return int(self.coords.real)
+    
+    @property
+    def y(self):
+        return int(self.coords.imag)
+    
+    @property
+    def neighbours(self):
+        yield from filter(None, (self.floor.get(self.coords + dir) for dir in Direction))
+
+def parse(data):
+    floor = {}
+
+    for y, line in enumerate(data.split('\n')):
+        for x, char in enumerate(line):
+            if char == '@':
+                floor[complex(real=x, imag=y)] = Paper(x, y, floor)
+    
+    return floor
+
+def is_accessible(paper):
+    return sum(1 for _ in paper.neighbours) < 4
+
+def main(data):
+    floor = parse(data.strip())
+    total = 0
+    while (removable := set(paper for paper in floor.values() if is_accessible(paper))):
+        total += len(removable)
+        for paper in removable:
+            del floor[paper.coords]
+    return total
+
+if __name__ == '__main__':
+    solution = main(aocd.get_data(day=4, year=2025))
+    print(solution)
+    aocd.submit(solution, part='b', day=4, year=2025)
\ No newline at end of file