Replace collecting then computing by reduce.

This is a bad idea; it's actually slower

2022/benches/days.rs

@@ -8,7 +8,7 @@ use criterion::BenchmarkId;
 use criterion::Criterion;
 
 /// Number of days we have an implementation to benchmark
-const DAYS_IMPLEMENTED: u8 = 0;
+const DAYS_IMPLEMENTED: u8 = 2;
 
 fn read_input(day: u8) -> Vec<u8> {
     let input_path = format!("inputs/{:02}.txt", day);

2022/src/common.rs

@@ -0,0 +1,94 @@
+//! Common helper utilities to all days
+
+use anyhow::Result;
+use nom::error::ErrorKind;
+use nom::error::ParseError;
+use nom::Finish;
+use nom::IResult;
+use nom::InputLength;
+use nom::Parser;
+
+/// Parse input from some nom parser and return as an anyhow result
+///
+/// This method exists as a convenience because nom's errors cannot otherwise be easily converted to
+/// an anyhow error, and I don't want to keep track of custom error implementations here.
+pub fn parse_input<'a, O>(
+    input: &'a [u8],
+    mut parser: impl Parser<&'a [u8], O, nom::error::Error<&'a [u8]>>,
+) -> Result<O> {
+    let (unparsed, output) = parser.parse(input).finish().map_err(|e| {
+        anyhow::anyhow!(
+            "Parser error {:?} to parse at {}",
+            e.code,
+            String::from_utf8_lossy(e.input)
+        )
+    })?;
+
+    if !unparsed.is_empty() {
+        Err(anyhow::anyhow!(
+            "Not all input consumed: {}",
+            String::from_utf8_lossy(unparsed)
+        ))
+    } else {
+        Ok(output)
+    }
+}
+
+/// Applies a parser iteratively and reduces the results using the given function. Fails if the
+/// embedded parser doesn't return at least one result.
+///
+/// # Arguments
+/// - `f`: the function to apply
+/// - `g`: the function that combines the result o `f` with previous results
+///
+/// This implementation is based on [`nom::multi::fold_many1`] with minor differences. If
+/// successful, this should probably be upstreamed.
+pub fn reduce_many1<I, O, E, F>(
+    mut f: F,
+    mut g: impl FnMut(O, O) -> O,
+) -> impl FnMut(I) -> IResult<I, O, E>
+where
+    I: Clone + InputLength,
+    E: ParseError<I>,
+    F: Parser<I, O, E>,
+{
+    // Cannot delegate to fold_many0 because that would make the function FnOnce rather than FnMut,
+    // since it would transfer ownership of the embedded parser to fold_many0.
+    move |i: I| {
+        let _i = i.clone();
+        match f.parse(_i) {
+            Err(nom::Err::Error(_)) => {
+                Err(nom::Err::Error(E::from_error_kind(i, ErrorKind::Many1)))
+            }
+            Err(e) => Err(e),
+            Ok((i1, mut acc)) => {
+                let mut input = i1;
+
+                loop {
+                    let _input = input.clone();
+                    let len = input.input_len();
+                    match f.parse(_input) {
+                        Err(nom::Err::Error(_)) => {
+                            break;
+                        }
+                        Err(e) => return Err(e),
+                        Ok((i, o)) => {
+                            // infinite loop check: the parser must always consume
+                            if i.input_len() == len {
+                                return Err(nom::Err::Failure(E::from_error_kind(
+                                    i,
+                                    ErrorKind::Many1,
+                                )));
+                            }
+
+                            acc = g(acc, o);
+                            input = i;
+                        }
+                    }
+                }
+
+                Ok((input, acc))
+            }
+        }
+    }
+}

2022/src/day01.rs

@@ -1,9 +1,55 @@
+use std::ops::Add;
+
 use anyhow::Result;
+use nom::character::complete::newline;
+use nom::combinator::opt;
+use nom::multi::separated_list0;
+use nom::sequence::terminated;
+use nom::IResult;
 
-pub fn part1(_input: &[u8]) -> Result<String> {
-    todo!()
+use crate::common::parse_input;
+use crate::common::reduce_many1;
+
+fn parse_elf(input: &[u8]) -> IResult<&[u8], i32> {
+    reduce_many1(terminated(nom::character::complete::i32, newline), Add::add)(input)
 }
 
-pub fn part2(_input: &[u8]) -> Result<String> {
-    todo!()
+fn parse_max(input: &[u8]) -> IResult<&[u8], i32> {
+    reduce_many1(terminated(parse_elf, opt(newline)), Ord::max)(input)
+}
+
+pub fn part1(input: &[u8]) -> Result<String> {
+    let result = parse_input(input, parse_max)?.to_string();
+    Ok(result)
+}
+
+fn parse_elf_list(input: &[u8]) -> IResult<&[u8], Vec<i32>> {
+    separated_list0(newline, parse_elf)(input)
+}
+
+pub fn part2(input: &[u8]) -> Result<String> {
+    let mut elves = parse_input(input, parse_elf_list)?;
+
+    let (first, third, _) = elves.select_nth_unstable_by(2, |a, b| Ord::cmp(b, a));
+
+    let result = first[1] + first[0] + *third;
+
+    Ok(result.to_string())
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    const SAMPLE: &[u8] = include_bytes!("samples/01.txt");
+
+    #[test]
+    fn sample_part1() {
+        assert_eq!(part1(SAMPLE).unwrap(), "24000");
+    }
+
+    #[test]
+    fn sample_part2() {
+        assert_eq!(part2(SAMPLE).unwrap(), "45000");
+    }
 }

2022/src/day02.rs

@@ -1,9 +1,129 @@
+use std::ops::Add;
+
 use anyhow::Result;
+use nom::character::complete::newline;
+use nom::combinator::map;
+use nom::combinator::map_res;
+use nom::sequence::separated_pair;
+use nom::sequence::terminated;
+use nom::IResult;
 
-pub fn part1(_input: &[u8]) -> Result<String> {
-    todo!()
+use crate::common::parse_input;
+use crate::common::reduce_many1;
+
+#[derive(Copy, Clone, Eq, PartialEq)]
+enum Rps {
+    Rock,
+    Paper,
+    Scissors,
 }
 
-pub fn part2(_input: &[u8]) -> Result<String> {
-    todo!()
+impl Rps {
+    /// Score we get by playing this move
+    fn score(self) -> u32 {
+        match self {
+            Rps::Rock => 1,
+            Rps::Paper => 2,
+            Rps::Scissors => 3,
+        }
+    }
+
+    /// Score we get from the result from playing given other
+    fn score_against(self, other: Self) -> u32 {
+        match (self, other) {
+            (a, b) if a == b => 3,
+            (Rps::Rock, Rps::Paper) | (Rps::Paper, Rps::Scissors) | (Rps::Scissors, Rps::Rock) => 0,
+            _ => 6,
+        }
+    }
+
+    /// Score if the result is according to the instruction
+    fn score_result(self) -> u32 {
+        match self {
+            Rps::Rock => 0,     // Rock is lose
+            Rps::Paper => 3,    // Paper is draw
+            Rps::Scissors => 6, // Scissors is win
+        }
+    }
+
+    /// Move we need to achieve the result indicated by self
+    fn needed(self, other: Self) -> Self {
+        match (self, other) {
+            (Rps::Paper, other) => other,
+            (Rps::Rock, Rps::Rock) => Rps::Scissors,
+            (Rps::Rock, Rps::Paper) => Rps::Rock,
+            (Rps::Rock, Rps::Scissors) => Rps::Paper,
+            (Rps::Scissors, Rps::Rock) => Rps::Paper,
+            (Rps::Scissors, Rps::Paper) => Rps::Scissors,
+            (Rps::Scissors, Rps::Scissors) => Rps::Rock,
+        }
+    }
+}
+
+impl TryFrom<u8> for Rps {
+    type Error = anyhow::Error;
+
+    fn try_from(value: u8) -> Result<Self, Self::Error> {
+        match value {
+            b'A' | b'X' => Ok(Rps::Rock),
+            b'B' | b'Y' => Ok(Rps::Paper),
+            b'C' | b'Z' => Ok(Rps::Scissors),
+            _ => Err(anyhow::anyhow!("Invalid RPS: {value}")),
+        }
+    }
+}
+
+fn parse_line(input: &[u8]) -> IResult<&[u8], (Rps, Rps)> {
+    fn parse_rps(input: &[u8]) -> IResult<&[u8], Rps> {
+        // Note: alpha1 also sort of works but is significantly slower
+        map_res(nom::bytes::complete::take(1usize), |v: &[u8]| {
+            Rps::try_from(v[0])
+        })(input)
+    }
+
+    terminated(
+        separated_pair(parse_rps, nom::character::complete::char(' '), parse_rps),
+        newline,
+    )(input)
+}
+
+pub fn part1(input: &[u8]) -> Result<String> {
+    parse_input(
+        input,
+        reduce_many1(
+            map(parse_line, |(them, us)| us.score() + us.score_against(them)),
+            Add::add,
+        ),
+    )
+    .map(|sum| sum.to_string())
+}
+
+pub fn part2(input: &[u8]) -> Result<String> {
+    parse_input(
+        input,
+        reduce_many1(
+            map(parse_line, |(them, us)| {
+                us.score_result() + us.needed(them).score()
+            }),
+            Add::add,
+        ),
+    )
+    .map(|sum| sum.to_string())
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    const SAMPLE: &[u8] = include_bytes!("samples/02.txt");
+
+    #[test]
+    fn sample_part1() {
+        assert_eq!(part1(SAMPLE).unwrap(), "15")
+    }
+
+    #[test]
+    fn sample_part2() {
+        assert_eq!(part2(SAMPLE).unwrap(), "12")
+    }
 }

2022/src/lib.rs

@@ -1,5 +1,6 @@
 use anyhow::Result;
 
+mod common;
 mod day01;
 mod day02;
 mod day03;

2022/src/samples/01.txt

@@ -0,0 +1,14 @@
+1000
+2000
+3000
+
+4000
+
+5000
+6000
+
+7000
+8000
+9000
+
+10000

2022/src/samples/02.txt

@@ -0,0 +1,3 @@
+A Y
+B X
+C Z