Implement 2022 day 1

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 = 1;
 
 fn read_input(day: u8) -> Vec<u8> {
     let input_path = format!("inputs/{:02}.txt", day);

2022/src/common.rs

@@ -0,0 +1,19 @@
+//! Common helper utilities to all days
+
+use anyhow::Result;
+use nom::Finish;
+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> {
+    match parser.parse(input).finish() {
+        Ok((_, value)) => Ok(value),
+        Err(err) => anyhow::bail!("Failed to parse at: {err:?}"),
+    }
+}

2022/src/day01.rs

@@ -1,9 +1,59 @@
+use std::ops::Add;
+
 use anyhow::Result;
+use nom::character::complete::newline;
+use nom::combinator::opt;
+use nom::multi::fold_many1;
+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;
+
+fn parse_elf(input: &[u8]) -> IResult<&[u8], i32> {
+    fold_many1(
+        terminated(nom::character::complete::i32, newline),
+        || 0,
+        Add::add,
+    )(input)
 }
 
-pub fn part2(_input: &[u8]) -> Result<String> {
-    todo!()
+fn parse_max(input: &[u8]) -> IResult<&[u8], i32> {
+    fold_many1(terminated(parse_elf, opt(newline)), || 0, 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/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