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 = 1;
+const DAYS_IMPLEMENTED: u8 = 2;
 
 fn read_input(day: u8) -> Vec<u8> {
     let input_path = format!("inputs/{:02}.txt", day);

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/samples/02.txt

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