Add description for day 16

day-16/day-16.py

@@ -3,8 +3,14 @@ from pathlib import Path
 from math import prod
 
 
-def get_next_packet(msg, start, packets, res=0):
+def get_next_packet(msg, idx, packets, res=0):
-    idx = start
+    """The function is called recursively and will read a single packet starting at index 'idx' in
+    'msg'. The packet will be appended to the 'packets' list. For each packet the type_id and a
+    payload is stored. The payload is a literal for packets of type 4 or will be filled with
+    subsequent packages for other types by recursion of this function. The version will be added to
+    the result.
+    At the end the updated index and result will be returned.
+    """
     if (idx+11) >= len(msg):
         idx = -1
         return idx, res
@@ -41,11 +47,12 @@ def get_next_packet(msg, start, packets, res=0):
                 next_idx = idx + length
                 while idx < next_idx:
                     idx, res = get_next_packet(msg, idx, payload, res)
-    packets.append({'version': version, 'type_id': type_id, 'payload': payload})
+    packets.append({'type_id': type_id, 'payload': payload})
     return idx, res
 
 
 def calc_result(packets):
+    """The function recursively steps through the packets and performs the defined calculations."""
     res = 0
     for p in packets:
         match p['type_id']:
@@ -74,6 +81,13 @@ def calc_result(packets):
 
 
 def solve(input):
+    """Part 1 and part 2 are solved in one go so we don't have to parse the bitstream twice. We
+    start by stripping newline and zeros at the end of the input line, convert it to an integer
+    with base 16 (hexadecimal) and back to a binary string. The bin() function adds '0b' at the
+    beginning so we only store te actual binary data. Afterwards we need to add zeros in the
+    beginning until the binary string has a length of four times the hexadecimal representation
+    (Each hex digit is four binary digits).
+    """
     result_p1 = 0
     line = input[0].rstrip().strip('0')
     msg = bin(int(line, 16))[2:]