From e75670eaf21246660fe401413b265da1c830deb9 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Anders=20Engl=C3=B6f=20Ytterstr=C3=B6m?= <yttan@fastmail.se>
Date: Sun, 8 Dec 2024 09:43:22 +0100
Subject: [PATCH] Solve 2016:21 p1-2 "Scrambled Letters and Hash"

A good day to utilize lots of unit testing!

For pt 2, the code initially tried to reverse
the scramble algorithm. The final code however
got the unscrambled version by the traditional
method most password crackers would resolve to:
basic brute forcing with permutations as a list
of candidates.
---
 2016-python2/output/day_21.py | 64 +++++++++++++++++++++++++++++++++++
 1 file changed, 64 insertions(+)
 create mode 100644 2016-python2/output/day_21.py

diff --git a/2016-python2/output/day_21.py b/2016-python2/output/day_21.py
new file mode 100644
index 0000000..d7eba1c
--- /dev/null
+++ b/2016-python2/output/day_21.py
@@ -0,0 +1,64 @@
+import re
+from itertools import permutations
+
+from output import ints
+
+
+def solve(data):
+    data = [line.strip() for line in data.splitlines()]
+    p1 = scramble(data, "abcdefgh")
+    p2 = unscramble(data, "fbgdceah")
+    return p1, p2
+
+
+def scramble(data, subject):
+    r_swap = r"(?:letter|position) (.)"
+    for line in data:
+        if line.startswith("rotate right"):
+            x = ints(line)[0]
+            subject = subject[-x:] + subject[:-x]
+        if line.startswith("rotate left"):
+            x = ints(line)[0]
+            subject = subject[x:] + subject[:x]
+        if line.startswith("rotate based"):
+            x = re.findall(r"letter (.)", line)[0]
+            i = subject.index(x)
+            j = i + 1 % len(subject)
+            subject = subject[-j:] + subject[:-j]
+            if i >= 4:
+                subject = subject[-1:] + subject[:-1]
+        if line.startswith("swap letter"):
+            x, y = re.findall(r_swap, line)
+            subject = subject.replace(y, "#")
+            subject = subject.replace(x, y)
+            subject = subject.replace("#", x)
+        if line.startswith("swap position"):
+            x, y = ints(line)
+            v1, v2 = subject[x], subject[y]
+            subject = subject[:x] + v2 + subject[x + 1 :]
+            subject = subject[:y] + v1 + subject[y + 1 :]
+        if line.startswith("move"):
+            x, y = ints(line)
+            v = subject[x]
+            subject = subject[:x] + subject[x + 1 :]
+            subject = subject[:y] + v + subject[y:]
+        if line.startswith("reverse"):
+            x, y = ints(line)
+            subject = subject[:x] + subject[x : y + 1][::-1] + subject[y + 1 :]
+    return subject
+
+
+def unscramble(data, T):
+    for candidate in ["".join(c) for c in permutations(T)]:
+        if scramble(data, candidate) == T:
+            return candidate
+
+
+if __name__ == "__main__":
+    with open("./input/21.txt", "r") as f:
+        inp = f.read().strip()
+
+    p1, p2 = solve(inp)
+
+    print(p1)
+    print(p2)