Solution to problem 1 in Python

src/Year_2017/P1.py

@@ -0,0 +1,105 @@
+# --- Day 1: Inverse Captcha ---
+
+# The night before Christmas, one of Santa's Elves calls you in a panic. "The
+# printer's broken! We can't print the Naughty or Nice List!" By the time you
+# make it to sub-basement 17, there are only a few minutes until midnight. "We
+# have a big problem," she says; "there must be almost fifty bugs in this
+# system, but nothing else can print The List. Stand in this square, quick!
+# There's no time to explain; if you can convince them to pay you in stars,
+# you'll be able to--" She pulls a lever and the world goes blurry.
+
+# When your eyes can focus again, everything seems a lot more pixelated than
+# before. She must have sent you inside the computer! You check the system
+# clock: 25 milliseconds until midnight. With that much time, you should be
+# able to collect all fifty stars by December 25th.
+
+# Collect stars by solving puzzles. Two puzzles will be made available on each
+# day millisecond in the Advent calendar; the second puzzle is unlocked when
+# you complete the first. Each puzzle grants one star. Good luck!
+
+# You're standing in a room with "digitization quarantine" written in LEDs
+# along one wall. The only door is locked, but it includes a small interface.
+# "Restricted Area - Strictly No Digitized Users Allowed."
+
+# It goes on to explain that you may only leave by solving a captcha to prove
+# you're not a human. Apparently, you only get one millisecond to solve the
+# captcha: too fast for a normal human, but it feels like hours to you.
+
+# The captcha requires you to review a sequence of digits (your puzzle input)
+# and find the sum of all digits that match the next digit in the list. The
+# list is circular, so the digit after the last digit is the first digit in the
+# list.
+
+# For example:
+
+#     1122 produces a sum of 3 (1 + 2) because the first digit (1) matches the
+# second digit and the third digit (2) matches the fourth digit.
+#     1111 produces 4 because each digit (all 1) matches the next.
+#     1234 produces 0 because no digit matches the next.
+#     91212129 produces 9 because the only digit that matches the next one is
+# the last digit, 9.
+
+# What is the solution to your captcha?
+
+with open("files/P1.txt") as f:
+    digits = [digit for digit in f.read().strip().split()]
+
+
+def part_1() -> None:
+    my_lst = iter(digits[0])
+    captcha = 0
+    current = next(my_lst)
+    # until exhausting the list
+    while (my_next := next(my_lst, None)) is not None:
+        if current == my_next:
+            captcha += int(current)
+        current = my_next
+
+    # in case first and last match:
+    if digits[0][0] == digits[0][-1]:
+        print(f"The solution (part 1) is {captcha + 1}")
+    else:
+        print(f"The solution (part 1) is {captcha}")
+
+
+# --- Part Two ---
+
+# You notice a progress bar that jumps to 50% completion. Apparently, the door
+# isn't yet satisfied, but it did emit a star as encouragement.
+# The instructions change:
+
+# Now, instead of considering the next digit, it wants you to consider the
+# digit halfway around the circular list. That is, if your list contains 10
+# items, only include a digit in your sum if the digit 10/2 = 5 steps forward
+# matches it. Fortunately, your list has an even number of elements.
+
+# For example:
+
+#     1212 produces 6: the list contains 4 items, and all four digits match the
+# digit 2 items ahead.
+#     1221 produces 0, because every comparison is between a 1 and a 2.
+#     123425 produces 4, because both 2s match each other, but no other digit
+# has a match.
+#     123123 produces 12.
+#     12131415 produces 4.
+
+# What is the solution to your new captcha?
+
+
+def part_2() -> None:
+    list_1 = digits[0]
+    list_2 = (
+        digits[0][int(len(digits[0]) / 2) :]
+        + digits[0][: int(len(digits[0]) / 2)]
+    )
+
+    captcha = 0
+    for el1, el2 in zip(list_1, list_2):
+        if el1 == el2:
+            captcha += int(el1)
+    print(f"The solution (part 2) is {captcha}")
+
+
+if __name__ == "__main__":
+    part_1()
+    part_2()