Implement 2022 day 11 part 1

2022/src/day11.rs

@@ -1,9 +1,146 @@
 use anyhow::Result;
+use nom::branch::alt;
+use nom::bytes::complete::tag;
+use nom::bytes::complete::take;
+use nom::character::complete::digit1;
+use nom::character::complete::newline;
+use nom::combinator::map;
+use nom::combinator::map_res;
+use nom::multi::separated_list0;
+use nom::multi::separated_list1;
+use nom::sequence::delimited;
+use nom::sequence::preceded;
+use nom::sequence::separated_pair;
+use nom::sequence::tuple;
+use nom::IResult;
 
-pub fn part1(_input: &[u8]) -> Result<String> {
-    anyhow::bail!("not implemented")
+use crate::common::parse_input;
+
+#[derive(Debug, Copy, Clone)]
+enum Operation {
+    Mul(u32),
+    Add(u32),
+    Square,
+}
+
+impl Operation {
+    fn transform(self, worry: u32) -> u32 {
+        match self {
+            Operation::Mul(val) => worry * val,
+            Operation::Add(val) => worry + val,
+            Operation::Square => worry * worry,
+        }
+    }
+}
+
+#[derive(Debug)]
+struct Monkey {
+    items: Vec<u32>,
+    operation: Operation,
+    test_mod: u32,
+    targets: [usize; 2],
+    inspected: usize,
+}
+
+impl Monkey {
+    fn handle_items(&mut self, drains: &mut [Vec<u32>; 2]) {
+        self.inspected += self.items.len();
+
+        for item in self.items.drain(..) {
+            let mut new_val = self.operation.transform(item);
+            // Miraculously get less worried
+            new_val /= 3;
+
+            drains[(new_val % self.test_mod == 0) as usize].push(new_val);
+        }
+    }
+}
+
+fn parse_operation(input: &[u8]) -> IResult<&[u8], Operation> {
+    preceded(
+        tag("new = old "),
+        alt((
+            map_res(
+                separated_pair(take(1usize), tag(" "), nom::character::complete::u32),
+                |(op, val): (&[u8], u32)| match op[0] {
+                    b'*' => Ok(Operation::Mul(val)),
+                    b'+' => Ok(Operation::Add(val)),
+                    _ => Err(anyhow::anyhow!("Invalid operation {op:?}")),
+                },
+            ),
+            map(tag("* old"), |_| Operation::Square),
+        )),
+    )(input)
+}
+
+fn parse_monkey(input: &[u8]) -> IResult<&[u8], Monkey> {
+    use nom::character::complete::u32;
+
+    map(
+        preceded(
+            // Skip the useless header line
+            tuple((tag("Monkey "), digit1, tag(":\n"))),
+            // Parse the actual interesting bits of the monkey
+            tuple((
+                // Parse the starting items
+                delimited(
+                    tag("  Starting items: "),
+                    separated_list1(tag(", "), u32),
+                    newline,
+                ),
+                // Parse operation
+                delimited(tag("  Operation: "), parse_operation, newline),
+                // Parse the test
+                delimited(tag("  Test: divisible by "), u32, newline),
+                // Parse both cases
+                delimited(tag("    If true: throw to monkey "), u32, newline),
+                delimited(tag("    If false: throw to monkey "), u32, newline),
+            )),
+        ),
+        |(items, operation, test_mod, if_true, if_false)| Monkey {
+            items,
+            operation,
+            test_mod,
+            targets: [if_false as usize, if_true as usize],
+            inspected: 0,
+        },
+    )(input)
+}
+
+pub fn part1(input: &[u8]) -> Result<String> {
+    let mut monkeys = parse_input(input, separated_list0(newline, parse_monkey))?;
+    let mut drains = [Vec::new(), Vec::new()];
+
+    for _ in 0..20 {
+        for i in 0..monkeys.len() {
+            monkeys[i].handle_items(&mut drains);
+
+            for j in 0..2 {
+                let target = monkeys[i].targets[j];
+                monkeys[target].items.append(&mut drains[j]);
+            }
+        }
+    }
+
+    monkeys.sort_by(|a, b| b.inspected.cmp(&a.inspected));
+
+    let result: usize = monkeys[0].inspected * monkeys[1].inspected;
+
+    Ok(result.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/11.txt");
+
+    #[test]
+    fn sample_part1() {
+        assert_eq!(part1(SAMPLE).unwrap(), "10605");
+    }
+}