[py] Port 2016_04, kinda

py/aoc/__init__.py

@@ -2,7 +2,7 @@ import sys
 import argparse
 from pathlib import Path
 
-from .y2016 import d01, d02, d03
+from .y2016 import d01, d02, d03, d04
 from .y2017 import d01, d02, d03, d04, d05, d06, d07, d08, d09
 from .y2018 import d01, d02, d03, d04, d05, d06, d07, d08, d09, d10, d11
 from .y2020 import d10
@@ -13,6 +13,7 @@ DAYS = {
     "2016_01": y2016.d01.solve,
     "2016_02": y2016.d02.solve,
     "2016_03": y2016.d03.solve,
+    "2016_04": y2016.d04.solve,
     "2017_01": y2017.d01.solve,
     "2017_02": y2017.d02.solve,
     "2017_03": y2017.d03.solve,

py/aoc/y2016/d04.py

@@ -0,0 +1,83 @@
+import re
+
+# PART 1
+
+ROOM_RE = r"(.*)-(\d+)\[(.{5})\]"
+
+
+def load_rooms(inputstr):
+    rooms = []
+    for line in inputstr.splitlines():
+        match = re.fullmatch(ROOM_RE, line)
+        name, sector, checksum = match.groups()
+        name = name.split("-")
+        sector = int(sector)
+        rooms.append((name, sector, checksum))
+    return rooms
+
+
+def checksum(name):
+    name = "".join(name)
+    freqs = {}
+    for char in name:
+        freqs[char] = freqs.get(char, 0) + 1
+
+    top = freqs.items()
+    top = sorted(top, key=lambda x: x[0])
+    top = sorted(top, key=lambda x: x[1], reverse=True)
+    top = list(top)[:5]
+    top = map(lambda x: x[0], top)
+    return "".join(top)
+
+
+def sum_correct_sectors(rooms):
+    total = 0
+    for name, sector, chk in rooms:
+        if checksum(name) == chk:
+            total += sector
+    return total
+
+
+# PART 2
+
+
+def shift(s):
+    new_s = []
+    for c in s:
+        if ord("a") <= ord(c) <= ord("z"):
+            new_c = chr(
+                ord("a") + ((ord(c) - ord("a") + 1) % (ord("z") - ord("a") + 1))
+            )
+            new_s.append(new_c)
+        elif ord("A") <= ord(c) <= ord("Z"):
+            new_c = chr(
+                ord("A") + ((ord(c) - ord("A") + 1) % (ord("Z") - ord("A") + 1))
+            )
+            new_s.append(new_c)
+        else:
+            new_s.append("?")
+    return "".join(new_s)
+
+
+def decrypt_name(name, sector):
+    for _ in range(sector % 26):
+        name = map(shift, name)
+    return " ".join(name)
+
+
+def decrypt_names(rooms, filename):
+    with open(filename, "w") as f:
+        for name, sector, chk in rooms:
+            if checksum(name) == chk:
+                name = decrypt_name(name, sector)
+                line = f"{name}-{sector}[{chk}]\n"
+                f.write(line)
+
+
+def solve(inputstr):
+    rooms = load_rooms(inputstr)
+    total = sum_correct_sectors(rooms)
+    print(f"Part 1: {total}")
+    # filename_2 = inputstr + ".decrypted"
+    # decrypt_names(rooms, filename_2)
+    # print(f"Part 2: see {filename_2} (search for 'northpole object storage')")