From 31bb5b7006946d68402ecd50a53b8b429f16b89b Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Anders=20Engl=C3=B6f=20Ytterstr=C3=B6m?= <yttan@fastmail.se>
Date: Fri, 29 Nov 2024 11:25:34 +0100
Subject: [PATCH] Solve 2016:14 p1-2 "One-Time Pad"

Lost 60 minutes due to misinterpreting this in p2:

> *whenever* you generate a hash

The code initially only did the 2016 stretching for
the triplet hash, not the quintet hash. By doing it
to both, pt 2 is solved.

Not sure the lru cache actually speeds anything up.
Many on the subreddit used the approach to generate
the quintet first and look backwards 1000 times
for a matching quintet (since quintets are more
rare than triplets), this will most likely speed
things up.

Also, this solution do not store the found keys.
Many other solutions do, I believe this is some
presumptions.
---
 2016-python2/output/day_14.py | 75 +++++++++++++++++++++++++++++++++++
 1 file changed, 75 insertions(+)
 create mode 100644 2016-python2/output/day_14.py

diff --git a/2016-python2/output/day_14.py b/2016-python2/output/day_14.py
new file mode 100644
index 0000000..01e96ae
--- /dev/null
+++ b/2016-python2/output/day_14.py
@@ -0,0 +1,75 @@
+import functools
+import re
+from hashlib import md5
+
+from output import answer  # , matrix, D, DD, ADJ, ints, mhd, mdbg, vdbg
+
+n = 14
+title = "One-Time Pad"
+
+
+@answer(1, "64th key is at index {}")
+def part_1(presolved):
+    return presolved[0]
+
+
+@answer(2, "64th key is at index {} using key stretching")
+def part_2(presolved):
+    return presolved[1]
+
+
+def solve(s):
+    p1 = run(s)
+    p2 = run(s, p2=True)
+    return p1, p2
+
+
+def run(s, p2=False):
+    r3 = re.compile(r"(\w)\1{2}")
+    c = 0
+    i = 0
+    H = md5(s.encode())
+    while True:
+        i += 1
+        if p2:
+            a = stretch(f"{s}{i}")
+        else:
+            Ha = H.copy()
+            Ha.update(str(i).encode())
+            a = Ha.hexdigest()
+        if m := re.search(r3, a):
+            x = m.group(1)
+            r5 = re.compile(r"(" + x + r")\1{4}")
+            for j in range(1000):
+                if p2:
+                    b = stretch(f"{s}{str(i + 1 + j)}")
+                else:
+                    Hb = H.copy()
+                    Hb.update(str(i + 1 + j).encode())
+                    b = Hb.hexdigest()
+                if re.search(r5, b):
+                    c += 1
+                    break
+        if c == 64:
+            break
+    return i
+
+
+@functools.lru_cache(maxsize=None)
+def stretch(s):
+    for _ in range(2017):
+        s = md5(s.encode()).hexdigest()
+    return s
+
+
+if __name__ == "__main__":
+    with open("./input/14.txt", "r") as f:
+        inp = f.read().strip()
+
+    inp = solve(inp)
+
+    a = part_1(inp)
+    b = part_2(inp)
+
+    assert a == 18626
+    assert b == 20092