From 14e8819b72e9159e6f29b25acb07fc685fb2d1d6 Mon Sep 17 00:00:00 2001
From: Thibaud <thibaud.gasser@gmx.com>
Date: Wed, 3 Jun 2026 18:36:27 +0200
Subject: [PATCH] 2015 day 11

---
 adventofcode/2015/day11/day11.py | 76 ++++++++++++++++++++++++++++++++
 1 file changed, 76 insertions(+)
 create mode 100644 adventofcode/2015/day11/day11.py

diff --git a/adventofcode/2015/day11/day11.py b/adventofcode/2015/day11/day11.py
new file mode 100644
index 0000000..a23be36
--- /dev/null
+++ b/adventofcode/2015/day11/day11.py
@@ -0,0 +1,76 @@
+#!/usr/bin/env python3
+import fileinput
+from itertools import islice
+
+
+def window(seq, n=3):
+    "Returns a sliding window (of width n) over data from the iterable"
+    "   s -> (s0,s1,...s[n-1]), (s1,s2,...,sn), ...                   "
+    it = iter(seq)
+    result = tuple(islice(it, n))
+    if len(result) == n:
+        yield result
+    for elem in it:
+        result = result[1:] + (elem,)
+        yield result
+
+
+def inc_string(s):
+    """
+    Increase the rightmost letter one step; if it was z, it wraps around to a,
+    and repeat with the next letter to the left until one doesn't wrap around.
+    """
+    s = list(s)
+    for i in range(len(s) - 1, -1, -1):
+        if s[i] == "z":
+            s[i] = "a"
+        else:
+            s[i] = chr(ord(s[i]) + 1)
+            break
+    return "".join(s)
+
+
+def is_valid(pwd):
+    """
+    A valid password:
+        - contains a increasing straight of three letters (abc, bcd, cde)
+        - contains two distinct pairs of letters (aa, bb, or zz).
+        - does not contain the letters i, o, or l.
+    """
+    has_forbiden_letters = any(x in "iol" for x in pwd)
+    pairs = set(pwd[i + 1] for i in range(len(pwd) - 1) if pwd[i] == pwd[i + 1])
+    has_two_pairs = len(pairs) == 2
+    has_increasing_triplet = False
+    for a, b, c in window(pwd):
+        a, b, c = ord(a), ord(b), ord(c)
+        if a + 1 == b and b + 1 == c:
+            has_increasing_triplet = True
+            break
+    is_valid = not has_forbiden_letters and has_two_pairs and has_increasing_triplet
+    return is_valid
+
+
+def get_next_valid_pwd(pwd):
+    while True:
+        pwd = inc_string(pwd)
+        if is_valid(pwd):
+            return pwd
+
+
+def main(pwd):
+    pwd = get_next_valid_pwd(pwd)
+    print("Part 1: ", pwd)
+    pwd = get_next_valid_pwd(pwd)
+    print("Part 2: ", pwd)
+
+
+def test():
+    assert inc_string("xx") == "xy"
+    assert inc_string("xy") == "xz"
+    assert inc_string("xz") == "ya"
+    assert inc_string("ya") == "yb"
+
+
+if __name__ == "__main__":
+    line = next(x.rstrip() for x in fileinput.input())
+    main(line)