Day 11

11.py

@@ -0,0 +1,38 @@
+#!/usr/bin/python
+
+from string import ascii_lowercase
+from itertools import takewhile
+import re
+
+input = 'cqjxjnds'
+
+run_regex = '|'.join(ascii_lowercase[i:i+3] for i in range(24))
+next_letter = dict((l, chr(ord(l) + 1)) for l in ascii_lowercase)
+next_letter['h'] = 'j'
+next_letter['n'] = 'p'
+next_letter['k'] = 'm'
+next_letter['z'] = 'a'
+
+
+def increment(str):
+    tail = sum(1 for _ in takewhile(lambda x: x == 'z', str[::-1]))
+    next = list(str)
+    if tail < len(next):
+        next[-tail - 1] = next_letter[next[-tail - 1]]
+    if tail > 0:
+        next[-tail:] = 'a' * tail
+    return ''.join(next)
+
+
+def matches(str):
+    has_run = re.search(run_regex, str)
+    has_bad_letters = re.search('[iol]', str)
+    has_pairs = re.search(r'(.)(\1).*?(?!\1)(.)(\3)', str)
+    return has_run and has_pairs and not has_bad_letters
+
+
+for _ in range(2):
+    input = increment(input)
+    while not matches(input):
+        input = increment(input)
+    print(input)