2021: d16: ex1: add solution

2021/d16/ex1/ex1.py

@@ -0,0 +1,138 @@
+#!/usr/bin/env python
+
+import enum
+import functools
+import itertools
+import sys
+from dataclasses import dataclass
+from typing import Iterable, Iterator, List, Tuple
+
+RawPacket = List[bool]
+
+
+class PacketType(enum.IntEnum):
+    SUM = 0
+    PRODUCT = 1
+    MINIMUM = 2
+    MAXIMUM = 3
+    LITTERAL = 4
+    GREATER = 5
+    LESS = 6
+    EQUAL = 7
+
+
+class PacketLengthType(enum.IntEnum):
+    TOTAL_BITS = 0  # Next 15 bits are the number of bits in the sub-packets
+    TOTAL_PACKETS = 1  # Next 11 bits are the number of sub-packets
+
+
+@dataclass
+class PacketLength:
+    type: PacketLengthType
+    length: int
+
+
+@dataclass
+class Packet:
+    version: int
+    type: PacketType
+
+
+@dataclass
+class OperatorPacket(Packet):
+    packets: List[Packet]
+
+
+@dataclass
+class LitteralPacket(Packet):
+    number: int
+
+
+def solve(input: List[str]) -> int:
+    def to_raw(packet: str) -> RawPacket:
+        def bits(n: int) -> Iterator[bool]:
+            for i in range(3, -1, -1):
+                yield bool(n & (1 << i))
+
+        nums = [int(c, 16) for c in input[0]]
+        return list(itertools.chain.from_iterable(bits(n) for n in nums))
+
+    def bits_to_int(bits: Iterable[bool]) -> int:
+        return functools.reduce(lambda a, b: (a << 1) + b, bits, 0)
+
+    def parse_packet(p: RawPacket) -> Tuple[int, Packet]:
+        def packet_version(p: RawPacket) -> int:
+            return bits_to_int(p[:3])
+
+        def packet_type(p: RawPacket) -> PacketType:
+            return PacketType(bits_to_int(p[3:6]))
+
+        def parse_length(p: RawPacket) -> Tuple[int, PacketLength]:
+            assert packet_type(p) != PacketType.LITTERAL  # Sanity check
+            type = PacketLengthType(bits_to_int(p[6:7]))
+            if type == PacketLengthType.TOTAL_BITS:
+                index = 7 + 15
+                length = bits_to_int(p[7:index])
+            else:
+                index = 7 + 11
+                length = bits_to_int(p[7:index])
+            return index, PacketLength(type, length)
+
+        def parse_litteral(p: RawPacket) -> Tuple[int, LitteralPacket]:
+            version, type = packet_version(p), packet_type(p)
+            assert type == PacketType.LITTERAL  # Sanity check
+            index = 6
+            bits: List[bool] = []
+            while True:
+                bits += p[index + 1 : index + 5]
+                index += 5
+                # Check if we were at the last one
+                if p[index - 5] == 0:
+                    break
+            return index, LitteralPacket(version, type, bits_to_int(bits))
+
+        def parse_operator(p: RawPacket) -> Tuple[int, OperatorPacket]:
+            version, type = packet_version(p), packet_type(p)
+            assert type != PacketType.LITTERAL  # Sanity check
+
+            index, length = parse_length(p)
+            packets: List[Packet] = []
+
+            if length.type == PacketLengthType.TOTAL_BITS:
+                sub_index = 0
+                while sub_index < length.length:
+                    parsed, packet = parse_packet(p[index:])
+                    sub_index += parsed
+                    index += parsed
+                    packets.append(packet)
+            else:
+                while len(packets) < length.length:
+                    parsed, packet = parse_packet(p[index:])
+                    index += parsed
+                    packets.append(packet)
+
+            return index, OperatorPacket(version, type, packets)
+
+        if packet_type(p) == PacketType.LITTERAL:
+            return parse_litteral(p)
+        return parse_operator(p)
+
+    def score(p: Packet) -> int:
+        if p.type == PacketType.LITTERAL:
+            return p.version
+        assert isinstance(p, OperatorPacket)  # Sanity check
+        return p.version + sum(score(c) for c in p.packets)
+
+    raw = to_raw(input[0])
+    __, packet = parse_packet(raw)
+
+    return score(packet)
+
+
+def main() -> None:
+    input = [line.strip() for line in sys.stdin.readlines()]
+    print(solve(input))
+
+
+if __name__ == "__main__":
+    main()