From 09d3f25b092e86df8be55114ddecb547a9c75c13 Mon Sep 17 00:00:00 2001
From: Julia Lange <public@julialange.org>
Date: Mon, 12 Jan 2026 11:43:49 -0800
Subject: [PATCH] 2025 04

---
 Python/2025/04/main.py | 47 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 47 insertions(+)
 create mode 100644 Python/2025/04/main.py

diff --git a/Python/2025/04/main.py b/Python/2025/04/main.py
new file mode 100644
index 0000000..78366d1
--- /dev/null
+++ b/Python/2025/04/main.py
@@ -0,0 +1,47 @@
+input = open("input", 'r')
+
+cardinal_offset = [x+y for x in [-1,0,1] for y in [-1j,0,1j] if x+y != 0]
+
+papermap = set()
+for x, line in enumerate(input):
+    for y, item in enumerate(line.rstrip()):
+        if item == "@":
+            papermap.add(complex(x,y))
+
+def part1(pmap, adjacent_min=4):
+    accessible = set()
+    for location in pmap:
+        adjacents = 0
+        for offset in cardinal_offset:
+            adjacents += 1 if location+offset in pmap else 0
+        if adjacents < adjacent_min:
+            accessible.add(location)
+    print(len(accessible))
+
+def part2(pmap, adjacent_min=4):
+    amap = {}
+    to_remove = set()
+    # Build adjacency map
+    for location in pmap:
+        adjacents = 0
+        for offset in cardinal_offset:
+            adjacents += 1 if location+offset in pmap else 0
+        amap[location] = adjacents
+        if adjacents < adjacent_min:
+            to_remove.add(location)
+    
+    starting_value = len(amap)
+
+    while to_remove:
+        rm_location = to_remove.pop()
+        del amap[rm_location]
+        for offset in cardinal_offset:
+            if rm_location+offset in amap:
+                amap[rm_location+offset] -= 1
+                if amap[rm_location+offset] < adjacent_min:
+                    to_remove.add(rm_location+offset)
+    
+    print(starting_value-len(amap))
+
+part1(papermap)
+part2(papermap)