2021 day16/rust: clean up

2021/data/day16.expected

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+904
+200476472872

2021/data/day16.input

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

2021/day16/day16_rs/Cargo.toml

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+[package]
+name = "day16_rs"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+nom = "7.1.0"

2021/day16/day16_rs/src/main.rs

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+#![warn(clippy::pedantic)]
+
+use std::{
+    io::{stdin, Read},
+    ops::ControlFlow,
+};
+
+use nom::{
+    bits::complete as bits,
+    multi::{many0, many_m_n},
+};
+use nom::{combinator::map, sequence::pair};
+use parsers::fold_till;
+
+mod parsers;
+
+type Input<'a> = (&'a [u8], usize);
+type IResult<'a, T> = nom::IResult<Input<'a>, T>;
+
+#[derive(Clone, Debug, PartialEq, Eq)]
+struct Packet {
+    version: u8,
+    typ: PacketType,
+}
+
+impl Packet {
+    pub fn parse(i: Input) -> IResult<Packet> {
+        map(
+            pair(bits::take(3_usize), PacketType::parse),
+            |(version, typ)| Packet { version, typ },
+        )(i)
+    }
+
+    pub fn version_sum(&self) -> usize {
+        usize::from(self.version)
+            + match self.typ {
+                PacketType::Literal(_) => 0,
+                PacketType::Operation {
+                    ref sub_packets, ..
+                } => sub_packets.iter().map(Packet::version_sum).sum(),
+            }
+    }
+}
+
+#[derive(Clone, Debug, PartialEq, Eq)]
+enum PacketType {
+    Literal(usize),
+    Operation {
+        operator: Operator,
+        sub_packets: Vec<Packet>,
+    },
+}
+
+impl PacketType {
+    pub fn parse(i: Input) -> IResult<PacketType> {
+        let (i, operator) = map(bits::take(3_usize), |type_id: u8| {
+            Operator::try_from(type_id)
+        })(i)?;
+
+        match operator {
+            Ok(operator) => map(Self::parse_sub_packets, |sub_packets| {
+                PacketType::Operation {
+                    operator,
+                    sub_packets,
+                }
+            })(i),
+            Err(_) => map(Self::parse_literal_value, PacketType::Literal)(i),
+        }
+    }
+
+    fn parse_sub_packets(i: Input) -> IResult<Vec<Packet>> {
+        enum LengthType {
+            Bits(usize),
+            Packets(usize),
+        }
+
+        impl LengthType {
+            pub fn parse(i: Input) -> IResult<Self> {
+                let (i, length_type_id) = bits::take(1_usize)(i)?;
+                match length_type_id {
+                    0 => map(bits::take(15_usize), LengthType::Bits)(i),
+                    1 => map(bits::take(11_usize), LengthType::Packets)(i),
+                    _ => unreachable!(),
+                }
+            }
+        }
+
+        let (i, length_type) = LengthType::parse(i)?;
+        match length_type {
+            LengthType::Packets(n) => many_m_n(n, n, Packet::parse)(i),
+            LengthType::Bits(n) => {
+                // manual implementation of something like the following:
+                // map_parser(recognize(bits::take(n)), many0(Packet::parse))(i)
+
+                let new_byte_offset = (n + i.1) / 8;
+                let new_bit_offset = (n + i.1) % 8;
+
+                let subpackets_input = (&i.0[..=new_byte_offset], i.1);
+                let (subpackets_end, subpackets) = many0(Packet::parse)(subpackets_input)?;
+
+                let new_input = (&i.0[new_byte_offset..], new_bit_offset);
+                assert_eq!(subpackets_end, new_input);
+
+                Ok((
+                    new_input,
+                    subpackets,
+                ))
+            }
+        }
+    }
+
+    fn parse_literal_value(i: Input) -> IResult<usize> {
+        fold_till(
+            pair(bits::take(1_usize), bits::take(4_usize)),
+            || 0,
+            |acc, (marker, bits): (u8, usize)| {
+                (if marker == 1 {
+                    ControlFlow::Continue
+                } else {
+                    ControlFlow::Break
+                })((acc << 4) | bits)
+            },
+        )(i)
+    }
+
+    pub fn evaluate(&self) -> usize {
+        match self {
+            Self::Literal(n) => *n,
+            Self::Operation {
+                operator,
+                sub_packets,
+            } => operator.evaluate(sub_packets.iter().map(|p| p.typ.evaluate())),
+        }
+    }
+}
+
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+enum Operator {
+    Sum,
+    Product,
+    Minimum,
+    Maximum,
+    GreaterThan,
+    LessThan,
+    EqualTo,
+}
+
+impl Operator {
+    pub fn evaluate(self, mut operands: impl Iterator<Item = usize>) -> usize {
+        match self {
+            Self::Sum => operands.sum(),
+            Self::Product => operands.product(),
+            Self::Minimum => operands.min().unwrap(),
+            Self::Maximum => operands.max().unwrap(),
+            Self::GreaterThan => usize::from(operands.next().unwrap() > operands.next().unwrap()),
+            Self::LessThan => usize::from(operands.next().unwrap() < operands.next().unwrap()),
+            Self::EqualTo => usize::from(operands.next().unwrap() == operands.next().unwrap()),
+        }
+    }
+}
+
+impl TryFrom<u8> for Operator {
+    type Error = ();
+
+    fn try_from(value: u8) -> Result<Self, Self::Error> {
+        match value {
+            0 => Ok(Self::Sum),
+            1 => Ok(Self::Product),
+            2 => Ok(Self::Minimum),
+            3 => Ok(Self::Maximum),
+            5 => Ok(Self::GreaterThan),
+            6 => Ok(Self::LessThan),
+            7 => Ok(Self::EqualTo),
+            _ => Err(()),
+        }
+    }
+}
+
+fn main() {
+    let bytes: Vec<u8> = stdin()
+        .lock()
+        .bytes()
+        .filter_map(|c| char::from(c.unwrap()).to_digit(16))
+        .map(|c| {
+            #[allow(clippy::cast_possible_truncation)] // a hex digit always fits in a u8
+            let c = c as u8;
+            c
+        })
+        .scan(None, |prev, n| {
+            Some(match *prev {
+                Some(i) => {
+                    *prev = None;
+                    Some(i | n)
+                }
+                None => prev.replace(n << 4),
+            })
+        })
+        .flatten()
+        .collect();
+
+    let packet = Packet::parse((&bytes, 0)).unwrap().1;
+    println!("{}", packet.version_sum());
+    println!("{}", packet.typ.evaluate());
+}

2021/day16/day16_rs/src/parsers.rs

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+use std::ops::ControlFlow;
+
+use nom::{
+    error::{ErrorKind, ParseError},
+    Err, InputLength, Parser,
+};
+
+pub fn fold_till<I, O, E, St, P, F, G>(
+    mut p: P,
+    mut init: F,
+    mut acc: G,
+) -> impl FnMut(I) -> nom::IResult<I, St, E>
+where
+    I: InputLength,
+    E: ParseError<I>,
+    P: Parser<I, O, E>,
+    F: FnMut() -> St,
+    G: FnMut(St, O) -> ControlFlow<St, St>,
+{
+    move |i| {
+        let mut res = init();
+        let mut input = i;
+
+        loop {
+            let len = input.input_len();
+            let (i, o) = p.parse(input)?;
+
+            if i.input_len() == len {
+                return Err(Err::Error(E::from_error_kind(i, ErrorKind::Many0)));
+            }
+
+            match acc(res, o) {
+                ControlFlow::Continue(next) => {
+                    res = next;
+                    input = i;
+                }
+                ControlFlow::Break(res) => return Ok((i, res)),
+            }
+        }
+    }
+}