1 files changed, 69 insertions, 0 deletions
diff --git a/11/solution.py b/11/solution.py
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index 0000000..5c044b3
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+++ b/11/solution.py
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+"""Advent of code 2015 day 11"""
+
+def next_password(password: str) -> str:
+    """Increment the password
+    "a" -> "b"
+    "az" -> "ba"
+    """
+    if password[-1] == 'z':
+        return next_password(password[:-1]) + 'a'
+    else:
+        return password[:-1] + chr(ord(password[-1]) + 1)
+
+def has_straight(password: str) -> bool:
+    """Check if a password contains a sequence of at least three consecutive characters"""
+    for i in range(len(password) - 2):
+        if ord(password[i]) + 1 == ord(password[i+1]) and ord(password[i+1]) + 1 == ord(password[i+2]):
+            return True
+    return False
+
+def has_pair(password: str) -> bool:
+    """Check if a password contains at least one pair of letters"""
+    for i in range(len(password) - 1):
+        if password[i] == password[i+1]:
+            return True
+    return False
+
+def has_pairs(password: str) -> bool:
+    """Check if a password contains at least two different, non-overlapping pairs of letters"""
+    for i in range(len(password) - 1):
+        if password[i] == password[i+1]:
+            return has_pair(password[i+2:])
+    return False
+
+def is_valid(password: str) -> bool:
+    """Check if password is valid
+    Password must:
+    - include one increasing straight of at least three letters
+    - may not contain i, o or l
+    - must contain at least two different, non-overlapping pairs of letters
+    "hijklmmn" -> False
+    "abbceffg" -> True
+    "abbcegjk" -> False
+    """
+    if not has_straight(password):
+        return False
+    if not has_pairs(password):
+        return False
+    if 'i' in password or 'o' in password or 'l' in password:
+        return False
+    return True
+
+def part1(password: str) -> str:
+    """Find the next valid password"""
+    password = next_password(password)
+    while not is_valid(password):
+        password = next_password(password)
+    return password
+
+def part2(password: str) -> str:
+    """Find the next valid password"""
+    password = next_password(part1(password))
+    while not is_valid(password):
+        password = next_password(password)
+    return password
+
+if __name__ == '__main__':
+    inp = 'cqjxjnds'
+    print(part1(inp))
+    print(part2(inp))