day 4

2025/04/solution.py

@@ -0,0 +1,94 @@
+#!/usr/bin/env python3
+import sys
+import pathlib
+
+def read_input():
+    path = pathlib.Path(sys.argv[1]) if len(sys.argv) > 1 else pathlib.Path("input.txt")
+    return path.read_text().rstrip("\n")
+
+def parse(data):
+    return data.splitlines()
+
+def part1(data):
+    total = 0
+
+    def surround(arr, x, y):
+        s = 0
+        def has(k, h):
+            nx = x + k
+            ny = y + h
+            if nx < 0 or nx >= len(arr):
+                return 0
+            if ny < 0 or ny >= len(arr[0]):
+                return 0
+            if arr[nx][ny] == '@':
+                return 1
+            return 0
+        s += has(-1, -1)
+        s += has(-1, 0)
+        s += has(-1, 1)
+        s += has(0, -1)
+        s += has(0, 1)
+        s += has(1, -1)
+        s += has(1, 0)
+        s += has(1, 1)
+        return s
+
+    for i in range(len(data)):
+        for j in range(len(data[0])):
+            if data[i][j] == '@':
+                cnt = surround(data, i, j)
+                if cnt < 4:
+                    total += 1
+    return total
+
+def part2(data):
+    total = 0
+
+    cpy = [list(row) for row in data]
+
+    def surround(arr, x, y):
+        s = 0
+        def has(k, h):
+            nx = x + k
+            ny = y + h
+            if nx < 0 or nx >= len(arr):
+                return 0
+            if ny < 0 or ny >= len(arr[0]):
+                return 0
+            if arr[nx][ny] == '@':
+                return 1
+            return 0
+        s += has(-1, -1)
+        s += has(-1, 0)
+        s += has(-1, 1)
+        s += has(0, -1)
+        s += has(0, 1)
+        s += has(1, -1)
+        s += has(1, 0)
+        s += has(1, 1)
+        return s
+
+    old = -1
+
+    while old != total:
+        old = total
+        for i in range(len(cpy)):
+            for j in range(len(cpy[0])):
+                if cpy[i][j] == '@':
+                    cnt = surround(cpy, i, j)
+                    if cnt < 4:
+                        cpy[i][j] = "x"
+                        total += 1
+    return total
+
+def main():
+    raw = read_input()
+    data = parse(raw)
+    r1 = part1(data)
+    r2 = part2(data)
+    print(r1)
+    print(r2)
+
+if __name__ == "__main__":
+    main()