Terribly inefficient part 1

2022/src/day19.rs

@@ -1,9 +1,188 @@
-use anyhow::Result;
+use std::ops::Add;
+use std::ops::Sub;
 
-pub fn part1(_input: &[u8]) -> Result<String> {
-    anyhow::bail!("not implemented")
+use anyhow::Result;
+use nom::bytes::complete::tag;
+use nom::character::complete::multispace1;
+use nom::character::streaming::alpha1;
+use nom::combinator::map_res;
+use nom::combinator::opt;
+use nom::multi::many1;
+use nom::sequence::delimited;
+use nom::sequence::preceded;
+use nom::sequence::separated_pair;
+use nom::sequence::terminated;
+use nom::sequence::tuple;
+use nom::IResult;
+
+use crate::common::parse_input;
+
+#[repr(usize)]
+#[derive(Clone, Copy)]
+enum Mineral {
+    Ore,
+    Clay,
+    Obsidian,
+    Geode,
+}
+
+impl TryFrom<&'_ [u8]> for Mineral {
+    type Error = String;
+
+    fn try_from(value: &'_ [u8]) -> std::result::Result<Self, Self::Error> {
+        dbg!(String::from_utf8_lossy(value));
+        match value {
+            b"ore" => Ok(Self::Ore),
+            b"clay" => Ok(Self::Clay),
+            b"obsidian" => Ok(Self::Obsidian),
+            b"geode" => Ok(Self::Geode),
+            other => Err(format!(
+                "Invalid mineral '{}'",
+                String::from_utf8_lossy(other)
+            )),
+        }
+    }
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Default)]
+struct Resources([u8; 4]);
+
+impl Resources {
+    fn enough_for(self, other: Self) -> bool {
+        self.0.iter().zip(&other.0).all(|(a, b)| a >= b)
+    }
+}
+
+impl Sub for Resources {
+    type Output = Self;
+
+    fn sub(self, rhs: Self) -> Self::Output {
+        Self(std::array::from_fn(|i| self.0[i] - rhs.0[i]))
+    }
+}
+
+impl Add<[u8; 4]> for Resources {
+    type Output = Self;
+
+    fn add(self, rhs: [u8; 4]) -> Self::Output {
+        Self(std::array::from_fn(|i| self.0[i] + rhs[i]))
+    }
+}
+
+#[derive(Debug)]
+struct BluePrint {
+    id: u32,
+    costs: [Resources; 4],
+}
+
+impl BluePrint {
+    pub fn max_geodes(&self) -> u8 {
+        self.max_geodes_recursive(24, 0, [1, 0, 0, 0], Resources::default())
+    }
+
+    fn max_geodes_recursive(
+        &self,
+        time_left: u32,
+        // forbidden is a bitset for convenience
+        forbidden: u8,
+        machines: [u8; 4],
+        resources: Resources,
+    ) -> u8 {
+        if time_left <= 1 {
+            return resources.0[3] + machines[3] * (time_left as u8);
+        }
+
+        let resources_after = resources + machines;
+
+        let mut best = 0;
+
+        let mut can_buy = 0;
+
+        for (i, &cost) in self.costs.iter().enumerate() {
+            if ((1 << i) & forbidden) == 0 && resources.enough_for(cost) {
+                can_buy |= 1 << i;
+                let mut new_machines = machines;
+                new_machines[i] += 1;
+
+                best = best.max(self.max_geodes_recursive(
+                    time_left - 1,
+                    0,
+                    new_machines,
+                    resources_after - cost,
+                ))
+            }
+        }
+
+        best.max(self.max_geodes_recursive(
+            time_left - 1,
+            forbidden | can_buy,
+            machines,
+            resources_after,
+        ))
+    }
+}
+
+fn parse_blueprint(input: &[u8]) -> IResult<&[u8], BluePrint> {
+    use nom::character::complete::u32;
+
+    fn parse_mineral(input: &[u8]) -> IResult<&[u8], Mineral> {
+        map_res(alpha1, Mineral::try_from)(input)
+    }
+
+    fn parse_cost(input: &[u8]) -> IResult<&[u8], (u8, Mineral)> {
+        separated_pair(nom::character::complete::u8, tag(" "), parse_mineral)(input)
+    }
+
+    let (mut input, id) =
+        terminated(delimited(tag("Blueprint "), u32, tag(":")), multispace1)(input)?;
+
+    let mut costs: [Resources; 4] = Default::default();
+
+    let mut parse_robot = terminated(
+        tuple((
+            preceded(tag("Each "), parse_mineral),
+            preceded(tag(" robot costs "), parse_cost),
+            terminated(opt(preceded(tag(" and "), parse_cost)), tag(".")),
+        )),
+        multispace1,
+    );
+
+    for _ in 0..4 {
+        let (remaining, (element, (amount1, req1), cost2)) = parse_robot(input)?;
+        input = remaining;
+
+        costs[element as usize].0[req1 as usize] = amount1;
+
+        if let Some((amount2, req2)) = cost2 {
+            costs[element as usize].0[req2 as usize] = amount2;
+        }
+    }
+
+    Ok((input, BluePrint { id, costs }))
+}
+
+pub fn part1(input: &[u8]) -> Result<String> {
+    let blueprints = parse_input(input, many1(parse_blueprint))?;
+
+    Ok(blueprints
+        .into_iter()
+        .map(|bp| dbg!(bp.max_geodes()) as u32 * bp.id)
+        .sum::<u32>()
+        .to_string())
 }
 
 pub fn part2(_input: &[u8]) -> Result<String> {
     anyhow::bail!("not implemented")
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    const SAMPLE: &[u8] = include_bytes!("./samples/19.txt");
+
+    #[test]
+    fn sample_part1() {
+        assert_eq!(part1(SAMPLE).unwrap(), "33");
+    }
+}