2021: day16: part 1
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025374e685
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78f059b65c
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@ -1,4 +1,5 @@
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use std::fmt::Write;
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use std::ops::Range;
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use anyhow::{Context, Result};
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use bitvec::prelude::*;
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@ -29,14 +30,18 @@ enum PacketType {
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struct Packet {
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version: u8,
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type_id: u8,
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bits_used: usize,
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packet: PacketType,
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}
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impl Packet {
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fn version_sum(&self) -> u64 {
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let version = self.version as u64;
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match &self.packet {
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PacketType::Litteral(_) => self.version as u64,
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PacketType::Operator(op) => op.sub_packets.iter().map(Packet::version_sum).sum(),
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PacketType::Litteral(_) => version,
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PacketType::Operator(op) => {
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version + op.sub_packets.iter().map(Packet::version_sum).sum::<u64>()
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}
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}
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}
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}
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@ -69,6 +74,20 @@ impl std::str::FromStr for Packet {
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}
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}
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const VERSION_RANGE: Range<usize> = 0..3;
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const TYPE_ID_RANGE: Range<usize> = 3..6;
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const TYPE_LENGTH_ID_INDEX: usize = 6;
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const LENGTH_INDEX: usize = 6 + 1;
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const TLID0_SUBPACKET_LENGTH_BITS: usize = 15;
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const SUBPACKET_START_INDEX_TLID0: usize = LENGTH_INDEX + TLID0_SUBPACKET_LENGTH_BITS;
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const SUBPACKETS_BIT_LENGTH_RANGE: Range<usize> = LENGTH_INDEX..SUBPACKET_START_INDEX_TLID0;
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const TLID1_SUBPACKET_NUMBER_BITS: usize = 11;
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const SUBPACKET_START_INDEX_TLID1: usize = LENGTH_INDEX + TLID1_SUBPACKET_NUMBER_BITS;
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const SUBPACKETS_NUMBER_RANGE: Range<usize> = LENGTH_INDEX..SUBPACKET_START_INDEX_TLID1;
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impl<'bits, Store> TryFrom<&'bits BitSlice<Msb0, Store>> for Packet
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where
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Store: BitStore,
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@ -76,17 +95,20 @@ where
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type Error = anyhow::Error;
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fn try_from(bits: &'bits BitSlice<Msb0, Store>) -> Result<Self> {
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let version: u8 = bits[0..3].load();
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let type_id: u8 = bits[3..6].load();
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let version: u8 = bits[VERSION_RANGE].load_be();
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let type_id: u8 = bits[TYPE_ID_RANGE].load_be();
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match type_id {
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// LitteralPacket
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4 => {
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let mut value = 0;
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let mut end = None;
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for i in (6..).step_by(5) {
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let val = bits[(i + 1)..(i + 5)].load::<u64>();
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let val = bits[(i + 1)..(i + 5)].load_be::<u64>();
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value = (value << 4) + val;
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if !bits[i] {
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end = Some(i + 5);
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break;
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}
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}
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@ -94,10 +116,45 @@ where
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Ok(Packet {
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version,
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type_id,
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bits_used: end.unwrap(),
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packet: PacketType::Litteral(LitteralPacket { value }),
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})
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}
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_ => unimplemented!("Operator packets aren't implemented yet"),
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// OperatorPacket
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_ => {
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let length_type_id = bits[TYPE_LENGTH_ID_INDEX];
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let mut sub_packets = Vec::new();
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let len = if length_type_id {
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let subpacket_num: usize = bits[SUBPACKETS_NUMBER_RANGE].load_be();
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let mut start_index = SUBPACKET_START_INDEX_TLID1;
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while sub_packets.len() < subpacket_num {
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let packet: Packet = bits[start_index..].try_into()?;
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start_index += packet.bits_used;
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sub_packets.push(packet);
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}
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start_index
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} else {
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let length: usize = bits[SUBPACKETS_BIT_LENGTH_RANGE].load_be();
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let mut start_index = SUBPACKET_START_INDEX_TLID0;
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while start_index != SUBPACKET_START_INDEX_TLID0 + length {
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let packet: Packet = bits[start_index..].try_into()?;
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start_index += packet.bits_used;
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sub_packets.push(packet);
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}
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SUBPACKET_START_INDEX_TLID0 + length
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};
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Ok(Packet {
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version,
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type_id,
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bits_used: len,
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packet: PacketType::Operator(OperatorPacket { sub_packets }),
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})
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}
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}
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}
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}
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@ -122,8 +179,75 @@ mod tests {
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Packet {
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version: 6,
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type_id: 4,
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bits_used: 21,
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packet: PacketType::Litteral(LitteralPacket { value: 2021 }),
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}
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);
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assert_eq!(
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PROVIDED2.parse::<Packet>().unwrap(),
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Packet {
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version: 1,
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type_id: 6,
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bits_used: 49,
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packet: PacketType::Operator(OperatorPacket {
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sub_packets: vec![
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Packet {
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version: 6,
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type_id: 4,
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bits_used: 11,
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packet: PacketType::Litteral(LitteralPacket { value: 10 })
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},
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Packet {
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version: 2,
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type_id: 4,
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bits_used: 16,
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packet: PacketType::Litteral(LitteralPacket { value: 20 })
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},
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],
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}),
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}
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);
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assert_eq!(
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PROVIDED3.parse::<Packet>().unwrap(),
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Packet {
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version: 7,
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type_id: 3,
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bits_used: 51,
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packet: PacketType::Operator(OperatorPacket {
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sub_packets: vec![
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Packet {
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version: 2,
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type_id: 4,
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bits_used: 11,
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packet: PacketType::Litteral(LitteralPacket { value: 1 })
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},
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Packet {
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version: 4,
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type_id: 4,
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bits_used: 11,
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packet: PacketType::Litteral(LitteralPacket { value: 2 })
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},
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Packet {
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version: 1,
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type_id: 4,
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bits_used: 11,
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packet: PacketType::Litteral(LitteralPacket { value: 3 })
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},
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],
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}),
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}
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);
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assert_eq!(PROVIDED4.parse::<Packet>().unwrap().version_sum(), 16);
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assert_eq!(PROVIDED5.parse::<Packet>().unwrap().version_sum(), 12);
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assert_eq!(PROVIDED6.parse::<Packet>().unwrap().version_sum(), 23);
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assert_eq!(PROVIDED7.parse::<Packet>().unwrap().version_sum(), 31);
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}
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#[test]
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fn part1_real() {
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assert_eq!(part1(INPUT).unwrap(), 925);
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}
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}
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