Solution to problem 4 in Python

src/Year_2019/P4.py

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+# --- Day 4: Secure Container ---
+
+# You arrive at the Venus fuel depot only to discover it's protected by a
+# password. The Elves had written the password on a sticky note, but someone
+# threw it out.
+
+# However, they do remember a few key facts about the password:
+
+#     It is a six-digit number.
+#     The value is within the range given in your puzzle input.
+#     Two adjacent digits are the same (like 22 in 122345).
+#     Going from left to right, the digits never decrease; they only ever
+# increase or stay the same (like 111123 or 135679).
+
+# Other than the range rule, the following are true:
+
+#     111111 meets these criteria (double 11, never decreases).
+#     223450 does not meet these criteria (decreasing pair of digits 50).
+#     123789 does not meet these criteria (no double).
+
+# How many different passwords within the range given in your puzzle input meet
+# these criteria?
+
+with open("files/P4.txt") as f:
+    a, b = [
+        int(number)
+        for line in f.read().strip().split()
+        for number in line.split("-")
+    ]
+
+
+def has_double_digits(number: int) -> bool:
+    number_str = str(number)
+    for a, b in zip(number_str, number_str[1:]):
+        if a == b:
+            return True
+    return False
+
+
+def never_decrease(number: int) -> bool:
+    number_str = str(number)
+    return all(int(x) <= int(y) for x, y in zip(number_str, number_str[1:]))
+
+
+def part_1() -> None:
+    count = 0
+    for number in range(a, b):
+        if has_double_digits(number):
+            if never_decrease(number):
+                count += 1
+
+    print(f"There are {count} different passwords")
+
+
+# --- Part Two ---
+
+# An Elf just remembered one more important detail: the two adjacent matching
+# digits are not part of a larger group of matching digits.
+
+# Given this additional criterion, but still ignoring the range rule, the
+# following are now true:
+
+#     112233 meets these criteria because the digits never decrease and all
+# repeated digits are exactly two digits long.
+#     123444 no longer meets the criteria (the repeated 44 is part of a larger
+# group of 444).
+#     111122 meets the criteria (even though 1 is repeated more than twice, it
+# still contains a double 22).
+
+# How many different passwords within the range given in your puzzle input meet
+# all of the criteria?
+
+
+def extra_detail(number: int) -> bool:
+    number_str = str(number)
+    for digit in number_str:
+        count = number_str.count(digit)
+        if count == 2:
+            return True
+    return False
+
+
+def part_2() -> None:
+    count = 0
+    for number in range(a, b):
+        if has_double_digits(number):
+            if never_decrease(number):
+                if extra_detail(number):
+                    count += 1
+
+    print(f"There are {count} different passwords")
+
+
+if __name__ == "__main__":
+    part_1()
+    part_2()