aoc

commit bc79fa83d3cb63d8445312b47dbed9295809b28a
parent 31c9f59a5f8946e8d90f2aad96e065ab4b496b67
Author: Sebastiano Tronto <sebastiano@tronto.net>
Date:   Thu,  4 Dec 2025 06:34:16 +0100

Day 4 2025

Diffstat:
M
2025/04/a.py
 | 
17
++++++++++++++++-
A
2025/04/b.py
 | 
26
++++++++++++++++++++++++++
M
2025/README.md
 | 
12
++++++++++++
M
README.md
 | 
2
+-

4 files changed, 55 insertions(+), 2 deletions(-)
diff --git a/2025/04/a.py b/2025/04/a.py
@@ -1,6 +1,21 @@
 import fileinput
 
+def neigh(a, i, j):
+	return [
+		a[i-1][j-1], a[i-1][j], a[i-1][j+1],
+		a[i][j-1],              a[i][j+1],
+		a[i+1][j-1], a[i+1][j], a[i+1][j+1],
+	].count('@')
+
+s = 0
 with fileinput.input() as lines:
+	a = [['.'] * 200]
 	for line in lines:
-		...
+		a.append(['.'] + list(line.replace('\n', '.')))
+	a.append(['.'] * 200)
 
+for i in range(1,len(a)-1):
+	for j in range(1,len(a[1])-1):
+		if a[i][j] == '@' and neigh(a, i, j) < 4:
+			s += 1
+print(s)
diff --git a/2025/04/b.py b/2025/04/b.py
@@ -0,0 +1,26 @@
+import fileinput
+
+def neigh(a, i, j):
+	return [
+		a[i-1][j-1], a[i-1][j], a[i-1][j+1],
+		a[i][j-1],              a[i][j+1],
+		a[i+1][j-1], a[i+1][j], a[i+1][j+1],
+	].count('@')
+
+s = 0
+with fileinput.input() as lines:
+	a = [['.'] * 200]
+	for line in lines:
+		a.append(['.'] + list(line.replace('\n', '.')))
+	a.append(['.'] * 200)
+
+rem = True
+while rem:
+	rem = False
+	for i in range(1,len(a)-1):
+		for j in range(1,len(a[1])-1):
+			if a[i][j] == '@' and neigh(a, i, j) < 4:
+				s += 1
+				rem = True
+				a[i][j] = '.'
+print(s)
diff --git a/2025/README.md b/2025/README.md
@@ -11,6 +11,7 @@ Example
 
 ```
 Day   -Part 1-   -Part 2-
+  4   00:25:36   00:27:49
   3   00:05:02   00:16:09
   2   00:10:36   00:11:55
   1   00:06:20   00:50:41
@@ -49,3 +50,14 @@ For part 2 I used recursion with memorization (using Python's
 `functools.cache`), which is fast enough. But later Chiara pointed
 out to me that actually the solution is quite trivially greedy; I
 implemented the greedy version in `b-alt.py`.
+
+### Day 4: Printing Department
+
+The first "map" problem of the year! This one was easy, but I
+made a lot of mistakes in part 1. I decided to use the trick that
+[Jared](https://guissmo.com) suggested a couple of years ago: extend the
+map by 1 cell in all directions so you don't have to deal with indices
+out of bounds.
+
+For part 2 I decided to quickly code the dumb "repeat part 1 until no
+rolls are removed" strategy and it worked.
diff --git a/README.md b/README.md
@@ -14,4 +14,4 @@ See `year/README.md` for instructions on how to run my code.
 |2022|  50 | Rust   | Done in 2025 to learn Rust |
 |2023|  50 | C      | All solved by December 25, 2023 |
 |2024|  50 | C++    | Each solved within 24h |
-|2025|  6  | Python | Work in progress... |
+|2025|  8  | Python | Work in progress... |