From 4681a782b5e0408534393f06bd18e24155c8f210 Mon Sep 17 00:00:00 2001
From: daviddoji <daviddoji@pm.me>
Date: Sun, 21 Jun 2026 20:32:51 +0200
Subject: [PATCH] Optimized solution

---
 src/Year_2015/P4.py | 47 ++++++++++++++++++++++++++++++---------------
 1 file changed, 31 insertions(+), 16 deletions(-)

diff --git a/src/Year_2015/P4.py b/src/Year_2015/P4.py
index 65f9508..23948ef 100644
--- a/src/Year_2015/P4.py
+++ b/src/Year_2015/P4.py
@@ -18,21 +18,30 @@
 # an MD5 hash starting with five zeroes is 1048970; that is, the MD5 hash of
 # pqrstuv1048970 looks like 000006136ef....
 
-# Your puzzle input is yzbqklnj.
 
 from hashlib import md5
+from itertools import count
 
-_input = "yzbqklnj"
+with open("files/P4.txt") as f:
+    secret_key = f.read().strip()
+
+key_bytes = secret_key.encode()
 
 
 def part_1() -> None:
-    end = "9" * len(_input)
-    for num in range(int(end)):
-        testing = _input + str(num)
-        result = md5(testing.encode()).hexdigest()
-        if result.startswith("0" * 5):
-            print(f"The lowest positive number is {num}")
-            break
+    padding = 5
+    prefix = "0" * padding
+    base_hash = md5(key_bytes)
+
+    for num in count(1):
+        digest_ctx = base_hash.copy()
+        digest_ctx.update(str(num).encode())
+        digest = digest_ctx.hexdigest()
+        if digest.startswith(prefix):
+            print(f"The lowest positive number starting with {padding} zeroes is {num}")
+            return
+
+    raise RuntimeError("No valid number found")
 
 
 # --- Part Two ---
@@ -41,13 +50,19 @@ def part_1() -> None:
 
 
 def part_2() -> None:
-    end = "9" * len(_input)
-    for num in range(int(end)):
-        testing = _input + str(num)
-        result = md5(testing.encode()).hexdigest()
-        if result.startswith("0" * 6):
-            print(f"The lowest positive number is {num}")
-            break
+    padding = 6
+    prefix = "0" * padding
+    base_hash = md5(key_bytes)
+
+    for num in count(1):
+        digest_ctx = base_hash.copy()
+        digest_ctx.update(str(num).encode())
+        digest = digest_ctx.hexdigest()
+        if digest.startswith(prefix):
+            print(f"The lowest positive number starting with {padding} zeroes is {num}")
+            return
+
+    raise RuntimeError("No valid number found")
 
 
 if __name__ == "__main__":