Day 19 - Part 2 WIP

Signed-off-by: Anthony Oteri <anthony.oteri@gmail.com>

day-19/src/part2.rs

@@ -1,8 +1,215 @@
+use std::collections::BTreeMap;
+
+use nom::{
+    branch::alt,
+    bytes::complete::tag,
+    character::complete,
+    combinator::{map, opt},
+    multi::{fold_many1, separated_list1},
+    sequence::{delimited, preceded, separated_pair, terminated},
+    IResult, Parser as _,
+};
+
 use crate::error::AocError;
 
+#[derive(Debug, Eq, PartialEq, Clone)]
+struct Workflow<'a> {
+    id: &'a str,
+    rules: Vec<Rule<'a>>,
+}
+
+#[derive(Debug, Clone, Eq, PartialEq)]
+enum Condition {
+    LessThen,
+    GreaterThen,
+}
+
+#[derive(Debug, Clone, Eq, PartialEq)]
+enum Target<'a> {
+    Workflow(&'a str),
+    Accept,
+    Reject,
+}
+
+#[derive(Debug, Clone, Eq, PartialEq)]
+enum Field {
+    X,
+    M,
+    A,
+    S,
+}
+
+#[derive(Debug, Clone, Eq, PartialEq)]
+enum Rule<'a> {
+    Test {
+        field: Field,
+        condition: Condition,
+        value: u16,
+        target: Target<'a>,
+    },
+    Target(Target<'a>),
+}
+
+impl<'a> Rule<'a> {
+    fn evaluate(&self, part: &'a Part) -> Option<Target<'a>> {
+        match self {
+            Rule::Test {
+                field,
+                condition,
+                value,
+                target,
+            } => {
+                let field_value = match field {
+                    Field::X => part.x,
+                    Field::M => part.m,
+                    Field::A => part.a,
+                    Field::S => part.s,
+                };
+                match condition {
+                    Condition::LessThen => {
+                        if field_value < *value {
+                            Some(target.clone())
+                        } else {
+                            None
+                        }
+                    }
+                    Condition::GreaterThen => {
+                        if field_value > *value {
+                            Some(target.clone())
+                        } else {
+                            None
+                        }
+                    }
+                }
+            }
+            Rule::Target(target) => Some(target.clone()),
+        }
+    }
+}
+
+fn rule(input: &str) -> IResult<&str, Rule> {
+    let (input, field) = complete::alpha1(input)?;
+    let (input, condition) = alt((
+        complete::char('<').map(|_| Condition::LessThen),
+        complete::char('>').map(|_| Condition::GreaterThen),
+    ))(input)?;
+    let (input, value) = complete::u16(input)?;
+    let (input, target) = preceded(complete::char(':'), target)(input)?;
+
+    Ok((
+        input,
+        Rule::Test {
+            field: match field {
+                "x" => Field::X,
+                "m" => Field::M,
+                "a" => Field::A,
+                "s" => Field::S,
+                _ => unreachable!(),
+            },
+            condition,
+            value,
+            target,
+        },
+    ))
+}
+
+fn target(input: &str) -> IResult<&str, Target> {
+    alt((
+        map(tag("A"), |_| Target::Accept),
+        map(tag("R"), |_| Target::Reject),
+        complete::alpha1.map(Target::Workflow),
+    ))(input)
+}
+
+fn workflow(input: &str) -> IResult<&str, Workflow> {
+    let (input, id) = complete::alpha1(input)?;
+    let (input, rules) = delimited(
+        complete::char('{'),
+        separated_list1(complete::char(','), alt((rule, target.map(Rule::Target)))),
+        complete::char('}'),
+    )(input)?;
+    Ok((input, Workflow { id, rules }))
+}
+
+fn workflows(input: &str) -> IResult<&str, BTreeMap<&str, Workflow>> {
+    let (input, workflows) = separated_list1(complete::line_ending, workflow)(input)?;
+    Ok((input, workflows.into_iter().map(|w| (w.id, w)).collect()))
+}
+
+#[derive(Debug, Clone, Eq, PartialEq, Default)]
+struct Part {
+    x: u16,
+    m: u16,
+    a: u16,
+    s: u16,
+}
+
+fn part(input: &str) -> IResult<&str, Part> {
+    delimited(
+        complete::char('{'),
+        fold_many1(
+            terminated(
+                separated_pair(complete::alpha1, complete::char('='), complete::u16),
+                opt(complete::char(',')),
+            ),
+            Part::default,
+            |mut part, (field, count)| {
+                match field {
+                    "x" => part.x = count,
+                    "m" => part.m = count,
+                    "a" => part.a = count,
+                    "s" => part.s = count,
+                    _ => unreachable!(),
+                }
+                part
+            },
+        ),
+        complete::char('}'),
+    )(input)
+}
+
+fn parse(input: &str) -> IResult<&str, (BTreeMap<&str, Workflow>, Vec<Part>)> {
+    let (input, workflows) = workflows(input)?;
+    let (input, _) = complete::multispace1(input)?;
+    let (input, parts) = separated_list1(complete::line_ending, part)(input)?;
+
+    Ok((input, (workflows, parts)))
+}
+
 #[tracing::instrument]
 pub fn process(input: &str) -> miette::Result<u64, AocError> {
-    Ok(0)
+    let (input, (workflows, _parts)) = parse(input).unwrap();
+    debug_assert!(input.is_empty(), "Should have parsed all the input");
+
+    let results = parts
+        .iter()
+        .filter_map(|part| {
+            let mut current = "in";
+            let target = 'outer: loop {
+                let active = workflows.get(current).unwrap();
+                'inner: for rule in &active.rules {
+                    match rule.evaluate(part) {
+                        Some(Target::Accept) => break 'outer Target::Accept,
+                        Some(Target::Reject) => break 'outer Target::Reject,
+                        Some(Target::Workflow(id)) => {
+                            current = id;
+                            break 'inner;
+                        }
+                        None => {}
+                    }
+                }
+            };
+            match target {
+                Target::Accept => {
+                    Some(part.x as u64 + part.m as u64 + part.a as u64 + part.s as u64)
+                }
+                Target::Reject => None,
+                _ => unreachable!(),
+            }
+        })
+        .sum::<u64>();
+
+    Ok(results)
 }
 
 #[cfg(test)]
@@ -12,7 +219,7 @@ mod tests {
     #[test_log::test]
     fn test_process() -> miette::Result<()> {
         let input = include_str!("../test-input.txt");
-        assert_eq!(0, process(input)?);
+        assert_eq!(167409079868000, process(input)?);
         Ok(())
     }
 }