2015: d11: ex2: add solution

2015/d11/ex2/ex2.py

@@ -0,0 +1,73 @@
+#!/usr/bin/env python
+
+import collections
+import itertools
+import sys
+from collections.abc import Iterable, Iterator
+from typing import TypeVar
+
+T = TypeVar("T")
+
+
+def sliding_window(iterable: Iterable[T], n: int) -> Iterator[tuple[T, ...]]:
+    iterator = iter(iterable)
+    window = collections.deque(itertools.islice(iterator, n - 1), maxlen=n)
+    for x in iterator:
+        window.append(x)
+        yield tuple(window)
+
+
+def solve(input: str) -> str:
+    def parse(input: str) -> int:
+        res = 0
+        for c in input.strip():
+            res = res * 26 + ord(c) - ord("a")
+        return res
+
+    def unparse(n: int) -> str:
+        # Passwords *must* have 8 characters
+        assert 0 <= n < 26**8  # Sanity check
+        return "".join(chr(ord("a") + (n // 26**i) % 26) for i in range(8))[::-1]
+
+    def has_straight(password: str) -> bool:
+        for a, b, c in sliding_window(password, 3):
+            if ord(a) + 1 == ord(b) and ord(b) + 1 == ord(c):
+                return True
+        return False
+
+    def no_iol(password: str) -> bool:
+        return not any(c in password for c in "iol")
+
+    def has_couples(password: str) -> bool:
+        for i, (a, b) in enumerate(itertools.pairwise(password)):
+            if a != b:
+                continue
+            for c, d in itertools.pairwise(password[i + 2 :]):
+                if c == d:
+                    return True
+            return False
+        return False
+
+    def next_password(password: str) -> str:
+        n = parse(password)
+        while True:
+            n = (n + 1) % 26**8  # Restrict password to 8 characters
+            password = unparse(n)
+            if not has_straight(password):
+                continue
+            if not no_iol(password):
+                continue
+            if not has_couples(password):
+                continue
+            return password
+
+    return next_password(next_password(input))
+
+
+def main() -> None:
+    input = sys.stdin.read()
+    print(solve(input))
+
+
+if __name__ == "__main__":
+    main()