Discover the magic of nom::combinator::value

2022/Cargo.toml

@@ -11,6 +11,7 @@ anyhow = "1.0.66"
 clap = { version = "4.0.19", features = ["derive"] }
 itertools = "0.10.5"
 nom = "7.1.1"
+strength_reduce = "0.2.4"
 
 [dev-dependencies]
 criterion = "0.4.0"

2022/inputs/11.txt

@@ -0,0 +1,55 @@
+Monkey 0:
+  Starting items: 84, 66, 62, 69, 88, 91, 91
+  Operation: new = old * 11
+  Test: divisible by 2
+    If true: throw to monkey 4
+    If false: throw to monkey 7
+
+Monkey 1:
+  Starting items: 98, 50, 76, 99
+  Operation: new = old * old
+  Test: divisible by 7
+    If true: throw to monkey 3
+    If false: throw to monkey 6
+
+Monkey 2:
+  Starting items: 72, 56, 94
+  Operation: new = old + 1
+  Test: divisible by 13
+    If true: throw to monkey 4
+    If false: throw to monkey 0
+
+Monkey 3:
+  Starting items: 55, 88, 90, 77, 60, 67
+  Operation: new = old + 2
+  Test: divisible by 3
+    If true: throw to monkey 6
+    If false: throw to monkey 5
+
+Monkey 4:
+  Starting items: 69, 72, 63, 60, 72, 52, 63, 78
+  Operation: new = old * 13
+  Test: divisible by 19
+    If true: throw to monkey 1
+    If false: throw to monkey 7
+
+Monkey 5:
+  Starting items: 89, 73
+  Operation: new = old + 5
+  Test: divisible by 17
+    If true: throw to monkey 2
+    If false: throw to monkey 0
+
+Monkey 6:
+  Starting items: 78, 68, 98, 88, 66
+  Operation: new = old + 6
+  Test: divisible by 11
+    If true: throw to monkey 2
+    If false: throw to monkey 5
+
+Monkey 7:
+  Starting items: 70
+  Operation: new = old + 7
+  Test: divisible by 5
+    If true: throw to monkey 1
+    If false: throw to monkey 3

2022/src/common.rs

@@ -1,5 +1,7 @@
 //! Common helper utilities to all days
 
+use std::cmp::Ordering;
+
 use anyhow::Result;
 use nom::combinator::map;
 use nom::error::ErrorKind;
@@ -116,3 +118,18 @@ where
         (b, a)
     }
 }
+
+/// Some magic to get two mutable references into the same slice
+pub fn get_both<T>(slice: &mut [T], first: usize, second: usize) -> (&mut T, &mut T) {
+    match first.cmp(&second) {
+        Ordering::Greater => {
+            let (begin, end) = slice.split_at_mut(first);
+            (&mut end[0], &mut begin[second])
+        }
+        Ordering::Less => {
+            let (begin, end) = slice.split_at_mut(second);
+            (&mut begin[first], &mut end[0])
+        }
+        Ordering::Equal => panic!("Tried to get the same index twice {first}"),
+    }
+}

2022/src/day05.rs

@@ -1,5 +1,3 @@
-use std::cmp::Ordering;
-
 use anyhow::Result;
 use nom::branch::alt;
 use nom::bytes::complete::tag;
@@ -8,6 +6,7 @@ use nom::bytes::complete::take_until;
 use nom::character::complete::newline;
 use nom::combinator::map;
 use nom::combinator::opt;
+use nom::combinator::value;
 use nom::multi::fold_many1;
 use nom::multi::many1;
 use nom::sequence::delimited;
@@ -17,6 +16,7 @@ use nom::sequence::tuple;
 use nom::IResult;
 
 use crate::common::enumerate;
+use crate::common::get_both;
 use crate::common::parse_input;
 
 type Move = (usize, usize, usize);
@@ -32,7 +32,7 @@ fn parse_row<'a>(input: &'a [u8], stacks: &mut OwnedStacks) -> IResult<&'a [u8],
                     Some(v[0])
                 }),
                 // Or an empty stack into a None
-                map(tag("   "), |_| None),
+                value(None, tag("   ")),
             )),
             opt(tag(" ")),
         )),
@@ -91,21 +91,6 @@ fn parse_task(input: &[u8]) -> IResult<&[u8], (OwnedStacks, Vec<Move>)> {
     Ok((input, (stacks, moves)))
 }
 
-/// Some magic to get two mutable references into the same slice
-fn get_both(stacks: &mut [Vec<u8>], from: usize, to: usize) -> (&mut Vec<u8>, &mut Vec<u8>) {
-    match from.cmp(&to) {
-        Ordering::Greater => {
-            let (begin, end) = stacks.split_at_mut(from);
-            (&mut end[0], &mut begin[to])
-        }
-        Ordering::Less => {
-            let (begin, end) = stacks.split_at_mut(to);
-            (&mut begin[from], &mut end[0])
-        }
-        Ordering::Equal => panic!("Tried to stack from and to {from}"),
-    }
-}
-
 fn compute_answer(stacks: &mut [Vec<u8>]) -> Result<String> {
     let mut result = String::with_capacity(stacks.len());
 

2022/src/day10.rs

@@ -4,6 +4,7 @@ use nom::bytes::complete::tag;
 use nom::character::complete::newline;
 use nom::combinator::iterator;
 use nom::combinator::map;
+use nom::combinator::value;
 use nom::sequence::preceded;
 use nom::sequence::terminated;
 use nom::IResult;
@@ -36,7 +37,7 @@ impl Instruction {
 fn parse_instruction(input: &[u8]) -> IResult<&[u8], Instruction> {
     terminated(
         alt((
-            map(tag("noop"), |_| Instruction::Noop),
+            value(Instruction::Noop, tag("noop")),
             map(preceded(tag("addx "), nom::character::complete::i32), |v| {
                 Instruction::AddX(v)
             }),

2022/src/day11.rs

@@ -1,9 +1,189 @@
 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::combinator::value;
+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;
+use strength_reduce::StrengthReducedU64;
 
-pub fn part1(_input: &[u8]) -> Result<String> {
-    anyhow::bail!("not implemented")
+use crate::common::parse_input;
+
+#[derive(Debug, Copy, Clone)]
+enum Operation {
+    Mul(u64),
+    Add(u64),
+    Square,
 }
 
-pub fn part2(_input: &[u8]) -> Result<String> {
-    anyhow::bail!("not implemented")
+impl Operation {
+    fn transform(self, worry: u64) -> u64 {
+        match self {
+            Operation::Mul(val) => worry * val,
+            Operation::Add(val) => worry + val,
+            Operation::Square => worry * worry,
+        }
+    }
+}
+
+#[derive(Debug)]
+struct Monkey {
+    items: Vec<u64>,
+    operation: Operation,
+    test_mod: StrengthReducedU64,
+    targets: [usize; 2],
+    inspected: usize,
+}
+
+impl Monkey {
+    fn handle_items(&mut self, drains: &mut [Vec<u64>; 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 handle_items2(&mut self, drains: &mut [Vec<u64>], mod_base: StrengthReducedU64) {
+        self.inspected += self.items.len();
+
+        for item in self.items.drain(..) {
+            let mut new_val = self.operation.transform(item);
+            // Modular arithmetic is a good way to get less worried
+            new_val = new_val % mod_base;
+
+            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::u64),
+                |(op, val): (&[u8], u64)| match op[0] {
+                    b'*' => Ok(Operation::Mul(val)),
+                    b'+' => Ok(Operation::Add(val)),
+                    _ => Err(anyhow::anyhow!("Invalid operation {op:?}")),
+                },
+            ),
+            value(Operation::Square, tag("* old")),
+        )),
+    )(input)
+}
+
+fn parse_monkey(input: &[u8]) -> IResult<&[u8], Monkey> {
+    use nom::character::complete::u64;
+
+    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(", "), u64),
+                    newline,
+                ),
+                // Parse operation
+                delimited(tag("  Operation: "), parse_operation, newline),
+                // Parse the test
+                delimited(tag("  Test: divisible by "), u64, newline),
+                // Parse both cases
+                delimited(tag("    If true: throw to monkey "), u64, newline),
+                delimited(tag("    If false: throw to monkey "), u64, newline),
+            )),
+        ),
+        |(items, operation, test_mod, if_true, if_false)| Monkey {
+            items,
+            operation,
+            test_mod: StrengthReducedU64::new(test_mod),
+            targets: [if_false as usize, if_true as usize],
+            inspected: 0,
+        },
+    )(input)
+}
+
+fn parse_monkeys(input: &[u8]) -> IResult<&[u8], Vec<Monkey>> {
+    separated_list0(newline, parse_monkey)(input)
+}
+
+fn format_result(mut monkeys: Vec<Monkey>) -> Result<String> {
+    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 part1(input: &[u8]) -> Result<String> {
+    let mut monkeys = parse_input(input, parse_monkeys)?;
+    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, drain) in drains.iter_mut().enumerate() {
+                let target = monkeys[i].targets[j];
+                monkeys[target].items.append(drain);
+            }
+        }
+    }
+
+    format_result(monkeys)
+}
+
+pub fn part2(input: &[u8]) -> Result<String> {
+    let mut monkeys = parse_input(input, parse_monkeys)?;
+    let mut drains = [Vec::new(), Vec::new()];
+
+    let mod_base = StrengthReducedU64::new(monkeys.iter().map(|m| m.test_mod.get()).product());
+
+    for _ in 0..10000 {
+        for i in 0..monkeys.len() {
+            monkeys[i].handle_items2(&mut drains, mod_base);
+
+            for (j, drain) in drains.iter_mut().enumerate() {
+                let target = monkeys[i].targets[j];
+                monkeys[target].items.append(drain);
+            }
+        }
+    }
+
+    format_result(monkeys)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    const SAMPLE: &[u8] = include_bytes!("samples/11.txt");
+
+    #[test]
+    fn sample_part1() {
+        assert_eq!(part1(SAMPLE).unwrap(), "10605");
+    }
+
+    #[test]
+    fn sample_part2() {
+        assert_eq!(part2(SAMPLE).unwrap(), "2713310158");
+    }
 }

2022/src/samples/11.txt

@@ -0,0 +1,27 @@
+Monkey 0:
+  Starting items: 79, 98
+  Operation: new = old * 19
+  Test: divisible by 23
+    If true: throw to monkey 2
+    If false: throw to monkey 3
+
+Monkey 1:
+  Starting items: 54, 65, 75, 74
+  Operation: new = old + 6
+  Test: divisible by 19
+    If true: throw to monkey 2
+    If false: throw to monkey 0
+
+Monkey 2:
+  Starting items: 79, 60, 97
+  Operation: new = old * old
+  Test: divisible by 13
+    If true: throw to monkey 1
+    If false: throw to monkey 3
+
+Monkey 3:
+  Starting items: 74
+  Operation: new = old + 3
+  Test: divisible by 17
+    If true: throw to monkey 0
+    If false: throw to monkey 1