Implement 2023 day 19 part 1

2023/src/day19.rs

@@ -1,7 +1,201 @@
-pub fn part1(_input: &[u8]) -> anyhow::Result<String> {
-    anyhow::bail!("Not implemented")
+use std::ops::Index;
+
+use nom::branch::alt;
+use nom::bytes::complete::tag;
+use nom::bytes::complete::take;
+use nom::bytes::complete::take_until1;
+use nom::bytes::complete::take_while1;
+use nom::combinator::map;
+use nom::multi::fold_many1;
+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;
+
+const RULES_LEN: usize = 26 * 26 * 26;
+
+#[derive(Clone, Copy)]
+struct Item([u16; 4]);
+
+impl Item {
+    fn rating_sum(self) -> u32 {
+        self.0.into_iter().map(u32::from).sum()
+    }
+
+    fn passes(&self, rules: &[Rule]) -> bool {
+        let mut pos = convert_name(b"in");
+
+        'outer: loop {
+            let rule = &rules[pos as usize];
+
+            for &(condition, end) in &rule.checks {
+                let is_valid = match condition {
+                    Condition::Greater(c, val) => self[c] > val,
+                    Condition::Less(c, val) => self[c] < val,
+                };
+
+                if is_valid {
+                    match end {
+                        RuleEnd::Reject => return false,
+                        RuleEnd::Accept => return true,
+                        RuleEnd::Next(new_pos) => {
+                            pos = new_pos;
+                            continue 'outer;
+                        }
+                    }
+                }
+            }
+
+            match rule.end {
+                RuleEnd::Reject => return false,
+                RuleEnd::Accept => return true,
+                RuleEnd::Next(new_pos) => {
+                    pos = new_pos;
+                    continue 'outer;
+                }
+            }
+        }
+    }
+}
+
+impl Index<u8> for Item {
+    type Output = u16;
+
+    fn index(&self, index: u8) -> &Self::Output {
+        static FALLBACK: u16 = 0;
+
+        match index {
+            b'x' => &self.0[0],
+            b'm' => &self.0[1],
+            b'a' => &self.0[2],
+            b's' => &self.0[3],
+            other => {
+                debug_assert!(false, "Invalid index: {}", other as char);
+                &FALLBACK
+            }
+        }
+    }
+}
+
+fn parse_item(i: &[u8]) -> IResult<&[u8], Item> {
+    use nom::character::complete::u16;
+    map(
+        tuple((
+            preceded(tag("{x="), u16),
+            preceded(tag(",m="), u16),
+            preceded(tag(",a="), u16),
+            delimited(tag(",s="), u16, tag("}\n")),
+        )),
+        |(x, m, a, s)| Item([x, m, a, s]),
+    )(i)
+}
+
+#[derive(Default, Copy, Clone)]
+enum RuleEnd {
+    #[default]
+    Reject,
+    Accept,
+    Next(u16),
+}
+
+#[derive(Clone, Copy)]
+enum Condition {
+    Greater(u8, u16),
+    Less(u8, u16),
+}
+
+#[derive(Default, Clone)]
+struct Rule {
+    checks: Vec<(Condition, RuleEnd)>,
+    end: RuleEnd,
+}
+
+// Base 26 at it again, but now in lowercase
+fn convert_name(name: &[u8]) -> u16 {
+    name.iter()
+        .fold(0, |cur, &c| cur * 26 + u16::from(c - b'a'))
+}
+
+fn parse_rule(i: &[u8]) -> IResult<&[u8], (u16, Rule)> {
+    fn convert_end(i: &[u8]) -> RuleEnd {
+        match i {
+            b"A" => RuleEnd::Accept,
+            b"R" => RuleEnd::Reject,
+            other => RuleEnd::Next(convert_name(other)),
+        }
+    }
+
+    let (i, name) = map(take_while1(|c: u8| c.is_ascii_alphabetic()), convert_name)(i)?;
+    let (i, _) = tag("{")(i)?;
+    let (i, checks) = many1(terminated(
+        map(
+            tuple((
+                take::<_, &[u8], _>(1usize),
+                alt((tag("<"), tag(">"))),
+                nom::character::complete::u16,
+                preceded(tag(":"), take_until1(",")),
+            )),
+            |(index, cmp, val, dest)| {
+                let condition = if cmp[0] == b'<' {
+                    Condition::Less(index[0], val)
+                } else {
+                    debug_assert_eq!(cmp[0], b'>');
+                    Condition::Greater(index[0], val)
+                };
+
+                (condition, convert_end(dest))
+            },
+        ),
+        tag(","),
+    ))(i)?;
+
+    let (i, end) = map(take_until1("}\n"), convert_end)(i)?;
+    Ok((&i[2..], (name, Rule { checks, end })))
+}
+
+fn parse_text(i: &[u8]) -> IResult<&[u8], (Box<[Rule]>, Vec<Item>)> {
+    separated_pair(
+        fold_many1(
+            parse_rule,
+            || vec![Rule::default(); RULES_LEN].into_boxed_slice(),
+            |mut rules, (index, rule)| {
+                rules[index as usize] = rule;
+                rules
+            },
+        ),
+        tag("\n"),
+        many1(parse_item),
+    )(i)
+}
+
+pub fn part1(input: &[u8]) -> anyhow::Result<String> {
+    let (rules, items) = parse_input(input, parse_text)?;
+
+    let passing = items
+        .iter()
+        .filter_map(|c| c.passes(&rules).then(|| c.rating_sum()))
+        .sum::<u32>();
+
+    Ok(passing.to_string())
 }
 
 pub fn part2(_input: &[u8]) -> anyhow::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!("19114", part1(SAMPLE).unwrap());
+    }
+}

2023/src/samples/19.txt

@@ -0,0 +1,17 @@
+px{a<2006:qkq,m>2090:A,rfg}
+pv{a>1716:R,A}
+lnx{m>1548:A,A}
+rfg{s<537:gd,x>2440:R,A}
+qs{s>3448:A,lnx}
+qkq{x<1416:A,crn}
+crn{x>2662:A,R}
+in{s<1351:px,qqz}
+qqz{s>2770:qs,m<1801:hdj,R}
+gd{a>3333:R,R}
+hdj{m>838:A,pv}
+
+{x=787,m=2655,a=1222,s=2876}
+{x=1679,m=44,a=2067,s=496}
+{x=2036,m=264,a=79,s=2244}
+{x=2461,m=1339,a=466,s=291}
+{x=2127,m=1623,a=2188,s=1013}