Implement day 18 2021

2021/benches/days.rs

@@ -7,7 +7,7 @@ use criterion::criterion_main;
 use criterion::BenchmarkId;
 use criterion::Criterion;
 
-const DAYS_IMPLEMENTED: usize = 16;
+const DAYS_IMPLEMENTED: usize = 18;
 
 fn read_input(day: usize) -> Vec<u8> {
     let input_path = format!("inputs/{:02}.txt", day);

2021/inputs/18.txt

@@ -0,0 +1,100 @@
+[[3,[[6,3],[9,6]]],[6,[[0,9],[9,7]]]]
+[[[3,9],[[0,8],[7,6]]],[[[7,9],1],[1,3]]]
+[8,[[[9,6],[8,4]],4]]
+[5,[[1,2],[3,7]]]
+[[[[7,7],5],[[3,5],8]],4]
+[[[5,[0,7]],3],[[5,[5,3]],[1,[9,4]]]]
+[[[[3,5],[7,1]],6],[[[3,6],[5,6]],[[3,2],5]]]
+[[[[2,0],[3,0]],[5,7]],[[4,4],[[9,9],[9,3]]]]
+[[[[8,0],7],[[7,1],9]],[[3,[8,6]],8]]
+[[6,[7,5]],[[6,8],9]]
+[[[9,[1,8]],2],[[[4,0],[9,3]],1]]
+[[7,[1,[3,8]]],[[4,7],[8,1]]]
+[[[5,5],[[4,5],[2,9]]],[[[7,7],0],8]]
+[[[[4,7],3],5],[[[4,3],[3,8]],[[6,5],5]]]
+[[[[3,8],2],[1,7]],[[[3,1],4],9]]
+[[[[2,1],4],[[9,5],[1,4]]],[[3,5],[[9,1],9]]]
+[[[6,[1,8]],[0,0]],[9,[0,3]]]
+[[[[2,2],[3,3]],[[4,8],4]],[[[6,8],4],5]]
+[4,[[[7,8],[3,4]],[[3,2],9]]]
+[[[9,0],3],[[[7,1],4],7]]
+[[[1,4],8],[[7,5],[[8,0],[0,7]]]]
+[9,[[4,6],[[2,9],1]]]
+[[[[1,8],8],6],[[[2,0],6],[0,5]]]
+[[[5,5],[6,4]],[[3,8],[9,[7,6]]]]
+[[0,[8,[1,4]]],2]
+[[[[9,5],0],5],[9,[7,5]]]
+[[9,[4,8]],[[8,1],[[8,6],[7,1]]]]
+[4,[[[9,6],5],9]]
+[[[[3,7],6],0],[[7,7],[[2,7],[9,3]]]]
+[[[6,[3,7]],[[8,3],2]],[8,[6,[8,5]]]]
+[[[5,[2,7]],[[6,7],3]],[5,[[4,4],1]]]
+[[1,0],[[2,8],[[0,4],9]]]
+[[[1,4],6],[[[9,8],[1,0]],1]]
+[[3,4],[[1,[8,4]],8]]
+[[[[9,4],[0,7]],[[5,4],[8,2]]],2]
+[5,[[[8,7],[3,4]],[2,4]]]
+[[[[1,3],[8,6]],[[3,4],6]],[[8,5],[[9,3],[5,7]]]]
+[[0,[[0,9],[7,8]]],[3,9]]
+[0,[[8,[2,3]],[[3,5],[4,9]]]]
+[[[4,3],[[1,9],[1,5]]],[4,[[9,1],1]]]
+[[[[3,6],[2,5]],3],[[8,[8,0]],[[6,9],[5,8]]]]
+[7,[[3,[3,6]],[[6,9],[2,7]]]]
+[[[[8,3],[6,5]],[[3,9],2]],[6,1]]
+[[[2,0],[2,3]],8]
+[[1,[[8,7],2]],[[[9,4],8],[4,[9,0]]]]
+[[[6,7],[[5,2],3]],[[0,5],[[9,4],[2,6]]]]
+[[[9,[5,8]],[[9,3],[6,9]]],5]
+[[[5,[4,6]],[5,[3,2]]],[2,[9,[5,4]]]]
+[8,6]
+[[[4,8],[3,1]],[1,[[7,8],[7,5]]]]
+[[4,[[8,8],4]],[5,[8,[3,9]]]]
+[[[4,[9,0]],[[0,3],5]],[[5,[3,0]],[6,[2,3]]]]
+[[[4,0],8],[[[4,0],7],[[9,6],3]]]
+[[8,[[7,8],5]],[[[6,2],8],[1,[0,4]]]]
+[[1,[[3,4],[0,8]]],[[6,5],3]]
+[[5,2],[[8,6],[1,[9,7]]]]
+[5,[6,[[1,3],[1,0]]]]
+[[0,[[1,9],[5,6]]],[[[6,2],[5,1]],[[1,2],[1,0]]]]
+[[[7,1],4],[[[0,3],3],[[4,8],1]]]
+[[3,[9,[3,4]]],[1,[[0,0],[1,4]]]]
+[1,[7,[1,[3,7]]]]
+[[[0,[5,6]],[[7,4],[5,7]]],[[[6,8],[4,6]],9]]
+[[[9,8],[7,[1,3]]],3]
+[[[4,[0,3]],[[3,0],6]],[[2,[9,2]],1]]
+[[[[1,9],[3,3]],[8,1]],5]
+[[7,[5,2]],[[4,[0,1]],[3,3]]]
+[[[6,6],[0,6]],[[3,[5,9]],[[4,2],[4,3]]]]
+[[[7,[5,4]],[7,1]],9]
+[[6,[5,2]],[[7,[0,5]],4]]
+[[[8,1],[[7,6],[4,1]]],2]
+[[[[4,3],[1,4]],[9,6]],[3,[[2,5],3]]]
+[[[[9,3],[5,0]],1],[1,[[9,7],9]]]
+[[[8,5],[5,9]],[2,[4,[0,0]]]]
+[[[[7,9],2],[[8,8],[6,3]]],[7,[0,9]]]
+[[[[6,6],[0,2]],[2,[9,0]]],[[0,9],[9,9]]]
+[[[9,[1,3]],[6,5]],[[[1,1],8],[9,[7,2]]]]
+[[8,[[8,4],6]],[[4,[5,9]],0]]
+[[8,[5,[6,7]]],[[[1,9],9],[0,[0,9]]]]
+[[9,[9,[7,3]]],[4,[4,7]]]
+[[[[9,3],7],5],[[5,[8,5]],[0,[8,0]]]]
+[[[5,[9,0]],[[7,4],[5,3]]],[3,[[1,1],[1,8]]]]
+[[1,[[1,4],[5,9]]],[[[9,1],[6,5]],[9,[0,7]]]]
+[[[[9,4],9],[5,3]],[[[4,2],[2,2]],[[1,0],0]]]
+[[[6,[8,6]],9],[8,[[0,1],[9,7]]]]
+[[2,0],[5,[[8,3],4]]]
+[[[[0,2],0],8],[8,[[2,5],[8,2]]]]
+[[[[7,4],8],[9,[7,5]]],[8,[7,[5,3]]]]
+[[2,4],[3,[3,8]]]
+[[5,4],[[0,[5,8]],[4,3]]]
+[6,[[5,[4,7]],9]]
+[[[2,[6,8]],[5,5]],[[[3,0],4],[[6,6],[0,1]]]]
+[[[1,[4,2]],[[8,0],8]],[8,[[6,1],[0,0]]]]
+[[9,[2,[3,3]]],[[2,6],[[5,2],[5,8]]]]
+[[9,[4,4]],[[[8,6],1],2]]
+[2,[[[0,7],7],[[7,8],5]]]
+[[[4,0],[[1,1],[7,6]]],[[6,7],[[7,2],1]]]
+[[[[2,5],0],[[9,5],9]],[6,[7,[6,1]]]]
+[[[7,8],1],[[[6,2],0],[[9,7],[3,5]]]]
+[[[9,1],0],[3,[[6,1],[6,9]]]]
+[[[[9,0],0],[4,[7,0]]],[[6,[4,0]],[8,[4,2]]]]

2021/src/common.rs

@@ -4,6 +4,9 @@ use std::io::Read;
 use std::marker::PhantomData;
 use std::str::FromStr;
 
+use nom::Finish;
+use nom::IResult;
+
 pub struct LineIter<'a> {
     reader: BufReader<&'a mut dyn Read>,
     buffer: String,
@@ -78,3 +81,15 @@ pub fn ordered<O: PartialOrd>(a: O, b: O) -> (O, O) {
         (b, a)
     }
 }
+
+pub fn read_input<P, O>(input: &mut dyn Read, parser: P) -> O
+where
+    P: for<'a> FnOnce(&'a [u8]) -> IResult<&'a [u8], O>,
+{
+    let mut buffer = Vec::new();
+    input.read_to_end(&mut buffer).unwrap();
+
+    let (_, output) = parser(&buffer).finish().unwrap();
+
+    output
+}

2021/src/day18.rs

@@ -1,9 +1,245 @@
+use std::fmt::Debug;
 use std::io::Read;
+use std::mem::replace;
 
-pub fn part1(_input: &mut dyn Read) -> String {
-    todo!()
+use nom::branch::alt;
+use nom::character::complete::newline;
+use nom::combinator::map;
+use nom::multi::many0;
+use nom::sequence::delimited;
+use nom::sequence::separated_pair;
+use nom::sequence::terminated;
+use nom::IResult;
+
+use crate::common::read_input;
+
+#[derive(Clone, Eq, PartialEq)]
+enum TurtleNumber {
+    Literal(u8),
+    Pair(Box<(TurtleNumber, TurtleNumber)>),
 }
 
-pub fn part2(_input: &mut dyn Read) -> String {
-    todo!()
+impl TurtleNumber {
+    pub fn add(self, other: Self) -> Self {
+        let mut new = TurtleNumber::Pair(Box::new((self, other)));
+        new.reduce();
+
+        new
+    }
+
+    pub fn magnitude(&self) -> u32 {
+        match self {
+            TurtleNumber::Literal(num) => *num as u32,
+            TurtleNumber::Pair(pair) => 3 * pair.0.magnitude() + 2 * pair.1.magnitude(),
+        }
+    }
+
+    fn reduce(&mut self) {
+        loop {
+            while self.try_explode(0).is_some() {}
+
+            if self.split() {
+                continue;
+            } else {
+                break;
+            }
+        }
+    }
+
+    fn leftmost_add(&mut self, value: u8) {
+        match self {
+            TurtleNumber::Literal(num) => *num += value,
+            TurtleNumber::Pair(pair) => pair.0.leftmost_add(value),
+        }
+    }
+
+    fn rightmost_add(&mut self, value: u8) {
+        match self {
+            TurtleNumber::Literal(num) => *num += value,
+            TurtleNumber::Pair(pair) => pair.1.rightmost_add(value),
+        }
+    }
+
+    fn try_explode(&mut self, depth: usize) -> Option<(Option<u8>, Option<u8>)> {
+        let pair = match self {
+            TurtleNumber::Literal(_) => return None,
+            TurtleNumber::Pair(pair) => pair,
+        };
+
+        if depth == 4 {
+            let original = replace(self, TurtleNumber::Literal(0));
+            let pair = match original {
+                TurtleNumber::Pair(pair) => *pair,
+                _ => unreachable!("Already checked for pair above"),
+            };
+
+            if let (TurtleNumber::Literal(first), TurtleNumber::Literal(second)) = pair {
+                Some((Some(first), Some(second)))
+            } else {
+                panic!("Too deeply nested turtle number: {:?}", pair);
+            }
+        } else {
+            match pair.0.try_explode(depth + 1) {
+                Some((left, Some(right))) => {
+                    pair.1.leftmost_add(right);
+                    Some((left, None))
+                }
+                Some((left, None)) => Some((left, None)),
+                None => match pair.1.try_explode(depth + 1) {
+                    Some((Some(left), right)) => {
+                        pair.0.rightmost_add(left);
+                        Some((None, right))
+                    }
+                    other => other,
+                },
+            }
+        }
+    }
+
+    pub fn split(&mut self) -> bool {
+        match self {
+            TurtleNumber::Literal(num) if *num >= 10 => {
+                let half = *num / 2;
+                let other = *num - half;
+                *self = TurtleNumber::from((half, other));
+                true
+            }
+            TurtleNumber::Pair(pair) => pair.0.split() || pair.1.split(),
+            _ => false,
+        }
+    }
+}
+
+impl Debug for TurtleNumber {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            Self::Literal(num) => write!(f, "{}", num),
+            Self::Pair(pair) => write!(f, "[{:?},{:?}]", pair.0, pair.1),
+        }
+    }
+}
+
+// Helper traits to easily convert tuples to turtle numbers
+impl From<u8> for TurtleNumber {
+    fn from(num: u8) -> Self {
+        TurtleNumber::Literal(num)
+    }
+}
+
+impl<T, U> From<(T, U)> for TurtleNumber
+where
+    T: Into<TurtleNumber>,
+    U: Into<TurtleNumber>,
+{
+    fn from((left, right): (T, U)) -> Self {
+        TurtleNumber::Pair(Box::new((left.into(), right.into())))
+    }
+}
+
+fn parse_turtle(input: &[u8]) -> IResult<&[u8], TurtleNumber> {
+    use nom::character::complete::char;
+    use nom::character::complete::u8;
+
+    alt((
+        map(u8, TurtleNumber::Literal),
+        map(
+            delimited(
+                char('['),
+                separated_pair(parse_turtle, char(','), parse_turtle),
+                char(']'),
+            ),
+            |pair| TurtleNumber::Pair(Box::new(pair)),
+        ),
+    ))(input)
+}
+
+fn parse_input(input: &[u8]) -> IResult<&[u8], Vec<TurtleNumber>> {
+    many0(terminated(parse_turtle, newline))(input)
+}
+
+pub fn part1(input: &mut dyn Read) -> String {
+    let turtles = read_input(input, parse_input);
+    turtles
+        .into_iter()
+        .reduce(|a, b| a.add(b))
+        .map(|num| num.magnitude())
+        .unwrap()
+        .to_string()
+}
+
+pub fn part2(input: &mut dyn Read) -> String {
+    let turtles = read_input(input, parse_input);
+
+    turtles
+        .iter()
+        .flat_map(|a| turtles.iter().map(|b| a.clone().add(b.clone()).magnitude()))
+        .max()
+        .unwrap()
+        .to_string()
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::test_implementation;
+
+    use super::*;
+
+    const SAMPLE: &[u8] = include_bytes!("samples/18.txt");
+
+    #[test]
+    fn test_magnitude() {
+        let num: TurtleNumber = (
+            (((8, 7), (7, 7)), ((8, 6), (7, 7))),
+            (((0, 7), (6, 6)), (8, 7)),
+        )
+            .into();
+
+        assert_eq!(num.magnitude(), 3488);
+    }
+
+    #[test]
+    fn test_add() {
+        let input = TurtleNumber::from(((((4, 3), 4), 4), (7, ((8, 4), 9))));
+        let result = input.add((1, 1).into());
+
+        let expected = TurtleNumber::from(((((0, 7), 4), ((7, 8), (6, 0))), (8, 1)));
+        assert_eq!(result, expected);
+    }
+
+    #[test]
+    fn test_explode() {
+        let mut input1 = TurtleNumber::from((((((9, 8), 1), 2), 3), 4));
+        let output1 = TurtleNumber::from(((((0, 9), 2), 3), 4));
+
+        input1.reduce();
+        assert_eq!(input1, output1);
+
+        let mut input2 = TurtleNumber::from((7, (6, (5, (4, (3, 2))))));
+        let output2 = TurtleNumber::from((7, (6, (5, (7, 0)))));
+
+        input2.reduce();
+        assert_eq!(input2, output2);
+
+        let mut input3: TurtleNumber = TurtleNumber::from(((6, (5, (4, (3, 2)))), 1));
+        let output3 = TurtleNumber::from(((6, (5, (7, 0))), 3));
+
+        input3.reduce();
+        assert_eq!(input3, output3);
+
+        let mut input4 = TurtleNumber::from(((3, (2, (1, (7, 3)))), (6, (5, (4, (3, 2))))));
+        let output4 = TurtleNumber::from(((3, (2, (8, 0))), (9, (5, (7, 0)))));
+
+        input4.reduce();
+        assert_eq!(input4, output4);
+    }
+
+    #[test]
+    fn sample_part1() {
+        test_implementation(part1, SAMPLE, 4140);
+    }
+
+    #[test]
+    fn sample_part2() {
+        test_implementation(part2, SAMPLE, 3993);
+    }
 }

2021/src/samples/18.txt

@@ -0,0 +1,10 @@
+[[[0,[5,8]],[[1,7],[9,6]]],[[4,[1,2]],[[1,4],2]]]
+[[[5,[2,8]],4],[5,[[9,9],0]]]
+[6,[[[6,2],[5,6]],[[7,6],[4,7]]]]
+[[[6,[0,7]],[0,9]],[4,[9,[9,0]]]]
+[[[7,[6,4]],[3,[1,3]]],[[[5,5],1],9]]
+[[6,[[7,3],[3,2]]],[[[3,8],[5,7]],4]]
+[[[[5,4],[7,7]],8],[[8,3],8]]
+[[9,3],[[9,9],[6,[4,9]]]]
+[[2,[[7,7],7]],[[5,8],[[9,3],[0,2]]]]
+[[[[5,2],5],[8,[3,7]]],[[5,[7,5]],[4,4]]]