Solution to problem 4 part 1 in Python

src/Year_2016/P4.py

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+# --- Day 4: Security Through Obscurity ---
+
+# Finally, you come across an information kiosk with a list of rooms. Of
+# course, the list is encrypted and full of decoy data, but the instructions to
+# decode the list are barely hidden nearby. Better remove the decoy data first.
+
+# Each room consists of an encrypted name (lowercase letters separated by
+# dashes) followed by a dash, a sector ID, and a checksum in square brackets.
+
+# A room is real (not a decoy) if the checksum is the five most common letters
+# in the encrypted name, in order, with ties broken by alphabetization. For
+# example:
+
+#     aaaaa-bbb-z-y-x-123[abxyz] is a real room because the most common letters
+# are a (5), b (3), and then a tie between x, y, and z, which are listed
+# alphabetically.
+#     a-b-c-d-e-f-g-h-987[abcde] is a real room because although the letters
+# are all tied (1 of each), the first five are listed alphabetically.
+#     not-a-real-room-404[oarel] is a real room.
+#     totally-real-room-200[decoy] is not.
+
+# Of the real rooms from the list above, the sum of their sector IDs is 1514.
+
+# What is the sum of the sector IDs of the real rooms?
+
+from collections import Counter
+from typing import Tuple
+
+with open("files/P4.txt") as f:
+    instructions = [line for line in f.read().strip().split()]
+
+
+def split_instruction(instr: str) -> Tuple[str, str, str]:
+    *name_, sector_id_checksum = str(instr).split("-")
+    name = "".join(name_)
+    sector_id, checksum = sector_id_checksum[:3], sector_id_checksum[4:-1]
+
+    return name, sector_id, checksum
+
+
+def part_1() -> None:
+    count = 0
+    for instruction in instructions:
+        name, sector_id, checksum = split_instruction(instruction)
+        # name must be sorted before counting due to problem requirements
+        chars = Counter(sorted(name))
+        checksum_calculated = "".join(n[0] for n in chars.most_common(5))
+        if checksum_calculated == checksum:
+            count += int(sector_id)
+
+    print(f"The sum is {count}")
+
+
+if __name__ == "__main__":
+    part_1()