Day 18 WIP, soo close.

2021/input/2021/day18.txt

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

2021/src/day18.rs

@@ -0,0 +1,732 @@
+use advent::prelude::*;
+use aoc_runner_derive::aoc;
+use std::{
+    io::{BufReader, Cursor, Read},
+    ops::Add,
+};
+
+#[derive(Copy, Clone, Debug, PartialEq)]
+enum ChildType {
+    None,
+    Value(usize),
+    Subtree(Idx),
+}
+
+#[derive(Copy, Clone, Default, PartialEq)]
+struct Idx(usize);
+
+impl Debug for Idx {
+    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
+        write!(f, "{}", self.0)
+    }
+}
+
+impl Display for Idx {
+    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
+        write!(f, "{}", self.0)
+    }
+}
+
+#[derive(Debug, PartialEq)]
+struct Node {
+    deleted: bool,
+    idx: Idx,
+    parent: Option<Idx>,
+    left: ChildType,
+    right: ChildType,
+}
+// Tree needs to support merging two into one for adding snailfish numbers.
+// Tree needs to support rightward and leftward depth first searches to find neighbors for applying
+// exploded spill over.
+// Need to support remove and/or replace for explode.
+// Need to support insert and/or replace for split.
+#[derive(Debug, Default)]
+struct Tree {
+    root: Idx,
+    nodes: Vec<Node>,
+}
+
+struct TreeIter {
+    it: std::vec::IntoIter<Idx>,
+}
+
+impl TreeIter {
+    fn new(indices: &[Idx]) -> TreeIter {
+        let indices = indices.to_vec();
+        TreeIter {
+            it: indices.into_iter(),
+        }
+    }
+}
+
+impl Iterator for TreeIter {
+    type Item = Idx;
+
+    fn next(&mut self) -> Option<Self::Item> {
+        self.it.next()
+    }
+}
+
+impl PartialEq for Tree {
+    fn eq(&self, other: &Self) -> bool {
+        // Lazy but should work.
+        self.to_string() == other.to_string()
+    }
+}
+
+fn read_byte<R: Read>(reader: &mut R) -> std::io::Result<Option<u8>> {
+    reader.bytes().next().transpose()
+}
+
+impl Tree {
+    fn reduce(&mut self) {
+        let mut changed = true;
+        while changed {
+            changed = self.explode();
+            println!("after explode {}", self);
+            if changed {
+                continue;
+            }
+            changed = self.split();
+            println!("after split {}", self);
+            //println!("splice changed {}", changed);
+        }
+    }
+    fn magnitude(&self) -> usize {
+        fn inner(tree: &Tree, node: &Node) -> usize {
+            match (node.left, node.right) {
+                (ChildType::Value(l), ChildType::Value(r)) => 3 * l + 2 * r,
+                (ChildType::Subtree(idx), ChildType::Value(r)) => {
+                    3 * inner(&tree, &tree[idx]) + 2 * r
+                }
+                (ChildType::Value(l), ChildType::Subtree(idx)) => {
+                    3 * l + 2 * inner(&tree, &tree[idx])
+                }
+                (ChildType::Subtree(l_idx), ChildType::Subtree(r_idx)) => {
+                    3 * inner(&tree, &tree[l_idx]) + 2 * inner(&tree, &tree[r_idx])
+                }
+                _ => panic!("unhandled combo for magnitude"),
+            }
+        }
+        inner(self, &self[self.root])
+    }
+
+    fn split(&mut self) -> bool {
+        if let Some(split_idx) = self
+            .left_to_right()
+            .skip_while(|idx| {
+                let n = &self[*idx];
+                if let ChildType::Value(v) = n.left {
+                    if v > 9 {
+                        return false;
+                    }
+                }
+                if let ChildType::Value(v) = n.right {
+                    if v > 9 {
+                        return false;
+                    }
+                }
+                true
+            })
+            .next()
+        {
+            if let ChildType::Value(v) = self[split_idx].left {
+                if v > 9 {
+                    let l = v / 2;
+                    let r = if v % 2 == 1 { 1 + v / 2 } else { v / 2 };
+                    let mut new_idx = self.add_node(ChildType::Value(l), ChildType::Value(r));
+                    self[new_idx].parent = Some(split_idx);
+                    self[split_idx].left = ChildType::Subtree(new_idx);
+                }
+            }
+            if let ChildType::Value(v) = self[split_idx].right {
+                if v > 9 {
+                    let l = v / 2;
+                    let r = if v % 2 == 1 { 1 + v / 2 } else { v / 2 };
+                    let mut new_idx = self.add_node(ChildType::Value(l), ChildType::Value(r));
+                    self[new_idx].parent = Some(split_idx);
+                    self[split_idx].right = ChildType::Subtree(new_idx);
+                }
+            }
+            return true;
+        }
+        false
+    }
+    fn explode(&mut self) -> bool {
+        let mut changed = false;
+        if let Some(node) = self
+            .nodes
+            .iter()
+            .filter(|n| !n.deleted)
+            .find(|n| self.depth(n) >= 4)
+        {
+            changed = true;
+            let ex_idx = node.idx;
+            // Find spillover to the right
+            if let Some(spillover) = self
+                .left_to_right()
+                .skip_while(|idx| *idx != ex_idx)
+                .skip(1)
+                .find(|idx| {
+                    let n = &self[*idx];
+                    match (n.left, n.right) {
+                        (ChildType::Subtree(_), ChildType::Subtree(_)) => false,
+                        _ => true,
+                    }
+                })
+            {
+                let src = self[ex_idx].right;
+                let tgt = &mut self[spillover];
+                if let (ChildType::Value(l), ChildType::Value(r)) = (src, tgt.left) {
+                    tgt.left = ChildType::Value(l + r);
+                } else if let (ChildType::Value(l), ChildType::Value(r)) = (src, tgt.right) {
+                    tgt.right = ChildType::Value(l + r);
+                } else {
+                    unreachable!()
+                };
+            }
+            // Find spillover to the left
+            if let Some(spillover) = self
+                .right_to_left()
+                .skip_while(|idx| *idx != ex_idx)
+                .skip(1)
+                .find(|idx| {
+                    let n = &self[*idx];
+                    match (n.left, n.right) {
+                        (ChildType::Subtree(_), ChildType::Subtree(_)) => false,
+                        _ => true,
+                    }
+                })
+            {
+                let src = self[ex_idx].left;
+                let tgt = &mut self[spillover];
+                if let (ChildType::Value(l), ChildType::Value(r)) = (src, tgt.right) {
+                    tgt.right = ChildType::Value(l + r);
+                } else if let (ChildType::Value(l), ChildType::Value(r)) = (src, tgt.left) {
+                    tgt.left = ChildType::Value(l + r);
+                } else {
+                    unreachable!()
+                };
+            }
+            // Replace exploded node
+            self[ex_idx].deleted = true;
+            let p_idx = self[ex_idx].parent.expect("exploded root");
+            let p = &mut self[p_idx];
+            if let ChildType::Subtree(idx) = p.left {
+                if idx == ex_idx {
+                    p.left = ChildType::Value(0);
+                }
+            }
+            if let ChildType::Subtree(idx) = p.right {
+                if idx == ex_idx {
+                    p.right = ChildType::Value(0);
+                }
+            }
+        }
+        changed
+    }
+    fn depth(&self, node: &Node) -> usize {
+        if let Some(parent_idx) = node.parent {
+            1 + self.depth(&self[parent_idx])
+        } else {
+            0
+        }
+    }
+    fn find_root(&self, node: &Node) -> Idx {
+        match node.parent {
+            Some(parent_idx) => self.find_root(&self[parent_idx]),
+            None => node.idx,
+        }
+    }
+    fn add_node(&mut self, left: ChildType, right: ChildType) -> Idx {
+        let idx = Idx(self.nodes.len());
+        self.nodes.push(Node {
+            deleted: false,
+            idx,
+            parent: None,
+            left,
+            right,
+        });
+        idx
+    }
+
+    fn from_str_node(&mut self, r: &mut BufReader<Cursor<&[u8]>>) -> ChildType {
+        let mut parsing_left = true;
+        // Can this be rewritten to eliminate the need for `None`?
+        let mut left = ChildType::None;
+        let mut right = ChildType::None;
+        while let Ok(Some(b)) = read_byte(r) {
+            match b {
+                b'[' => {
+                    let node = self.from_str_node(r);
+                    if parsing_left {
+                        left = node;
+                    } else {
+                        right = node;
+                    }
+                }
+                b']' => {
+                    let mut left_idx = None;
+                    let mut right_idx = None;
+                    if let ChildType::Subtree(idx) = left {
+                        left_idx = Some(idx);
+                    }
+                    if let ChildType::Subtree(idx) = right {
+                        right_idx = Some(idx);
+                    }
+                    let child_idx = self.add_node(left, right);
+                    if let Some(idx) = left_idx {
+                        self[idx].parent = Some(child_idx);
+                    }
+                    if let Some(idx) = right_idx {
+                        self[idx].parent = Some(child_idx);
+                    }
+                    return ChildType::Subtree(child_idx);
+                }
+                b',' => parsing_left = false,
+                b'0'..=b'9' => {
+                    let mut v = b - b'0';
+                    if let Ok(Some(peek)) = read_byte(r) {
+                        match peek {
+                            b'0'..=b'9' => v = (peek - b'0') + 10 * v,
+                            // Wasn't a number >9, push the byte back into the buffer.
+                            _ => r.seek_relative(-1).expect("failed to seek"),
+                        }
+                    }
+                    if parsing_left {
+                        left = ChildType::Value(v.into());
+                        parsing_left = false;
+                    } else {
+                        right = ChildType::Value(v.into());
+                    }
+                    continue;
+                }
+                _ => panic!("unknown byte '{}'", b),
+            }
+        }
+        unreachable!()
+    }
+
+    fn fmt_node(&self, f: &mut Formatter<'_>, node: &Node) -> std::fmt::Result {
+        write!(f, "[")?;
+        match node.left {
+            ChildType::None => panic!("left node was None"),
+            ChildType::Value(v) => write!(f, "{}", v)?,
+            ChildType::Subtree(idx) => self.fmt_node(f, &self[idx])?,
+        };
+        write!(f, ",")?;
+        match node.right {
+            ChildType::None => panic!("right node was None"),
+            ChildType::Value(v) => write!(f, "{}", v)?,
+            ChildType::Subtree(idx) => self.fmt_node(f, &self[idx])?,
+        };
+        write!(f, "]")?;
+        Ok(())
+    }
+
+    fn left_to_right(&mut self) -> TreeIter {
+        fn dfs(tree: &Tree, n: &Node, mut indices: &mut Vec<Idx>) {
+            if let ChildType::Subtree(idx) = n.left {
+                dfs(tree, &tree[idx], indices);
+            }
+            indices.push(n.idx);
+            if let ChildType::Subtree(idx) = n.right {
+                dfs(tree, &tree[idx], indices);
+            }
+        }
+        let mut indices = Vec::with_capacity(self.nodes.len());
+        dfs(self, &self[self.root], &mut indices);
+        TreeIter::new(&indices)
+    }
+    fn right_to_left(&mut self) -> TreeIter {
+        fn dfs(tree: &Tree, n: &Node, mut indices: &mut Vec<Idx>) {
+            if let ChildType::Subtree(idx) = n.right {
+                dfs(tree, &tree[idx], indices);
+            }
+            indices.push(n.idx);
+            if let ChildType::Subtree(idx) = n.left {
+                dfs(tree, &tree[idx], indices);
+            }
+        }
+        let mut indices = Vec::with_capacity(self.nodes.len());
+        dfs(self, &self[self.root], &mut indices);
+        TreeIter::new(&indices)
+    }
+}
+
+impl Add for Tree {
+    type Output = Tree;
+
+    fn add(self, other: Self) -> Self {
+        // This is lazy but works for simple any obvious reasons (if FromStr and Display work
+        // correctly).
+        format!("[{},{}]", self, other)
+            .parse()
+            .expect("failed to parse merge tree")
+    }
+}
+
+impl FromStr for Tree {
+    type Err = Infallible;
+
+    fn from_str(input: &str) -> std::result::Result<Tree, Infallible> {
+        let mut tree = Tree::default();
+        let mut bytes = input.as_bytes();
+        assert_eq!(
+            read_byte(&mut bytes).expect("couldn't read first byte"),
+            Some(b'[')
+        );
+        let mut b = BufReader::new(Cursor::new(bytes));
+        tree.from_str_node(&mut b);
+        tree.root = tree.find_root(&tree[Idx(0)]);
+        Ok(tree)
+    }
+}
+
+impl Index<Idx> for Tree {
+    type Output = Node;
+    fn index(&self, idx: Idx) -> &Self::Output {
+        &self.nodes[idx.0]
+    }
+}
+
+impl IndexMut<Idx> for Tree {
+    fn index_mut(&mut self, idx: Idx) -> &mut Self::Output {
+        &mut self.nodes[idx.0]
+    }
+}
+
+impl Display for Tree {
+    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
+        if self.nodes.is_empty() {
+            return write!(f, "[]");
+        }
+
+        let node = &self[self.root];
+        self.fmt_node(f, &node)?;
+        Ok(())
+    }
+}
+
+fn sum(input: &str) -> Tree {
+    input
+        .lines()
+        .map(|l| l.parse().expect("failed to parse"))
+        .reduce(|acc, t| acc + t)
+        .expect("failed to reduce")
+}
+
+#[aoc(day18, part1)]
+fn part1(input: &str) -> Result<usize> {
+    let nums: Vec<Tree> = input
+        .lines()
+        .map(|l| {
+            dbg!(l);
+            l.parse().expect("failed to parse")
+        })
+        .collect();
+    let mut it = nums.into_iter();
+    let mut last = it.next().unwrap();
+    while let Some(next) = it.next() {
+        println!("  {}", last);
+        println!("+ {}", next);
+        last = last + next;
+        println!("= {}", last);
+        last.reduce();
+        println!("= {}\n", last);
+    }
+    Ok(last.magnitude())
+}
+
+/*
+#[aoc(day18, part2)]
+fn part2(input: &str) -> Result<usize> {
+todo!("part2");
+Ok(0)
+}
+*/
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_display() -> Result<()> {
+        for (i, s) in ["[1,2]", "[[1,2],3]", "[1,[2,3]]", "[[1,2],[3,4]]"]
+            .into_iter()
+            .enumerate()
+        {
+            let t = s.parse::<Tree>()?;
+            assert_eq!(&t.to_string(), s, "input {}: '{}'", i, s);
+            //assert_eq!(&t.to_string(), s, "input {}: '{}'\ntree: {:#?}", i, s, t);
+        }
+        Ok(())
+    }
+
+    #[test]
+    fn test_sum() -> Result<()> {
+        let l: Tree = "[1,2]".parse().unwrap();
+        let r: Tree = "[[3,4],5]".parse().unwrap();
+        assert_eq!(l + r, "[[1,2],[[3,4],5]]".parse().unwrap());
+
+        let input = r#"
+[[[[4,3],4],4],[7,[[8,4],9]]]
+[1,1]
+    "#
+        .trim();
+        let mut s = sum(input);
+        s.reduce();
+        assert_eq!(s.to_string(), "[[[[0,7],4],[[7,8],[6,0]]],[8,1]]");
+        Ok(())
+    }
+
+    #[test]
+    fn test_reduce() -> Result<()> {
+        for (input, want) in [
+            ("[0,[0,[0,[0,[0,0]]]]]", "[0,[0,[0,[0,0]]]]"),
+            ("[[[[[[[[0,0],0],0],0],0],0],0],0]", "[[[[0,0],0],0],0]"),
+            ("[[[[[[[0,0],0],0],0],0],0],0]", "[[[[0,0],0],0],0]"),
+        ] {
+            println!("== test_reduce: {}", input);
+            let mut tree: Tree = input.parse()?;
+            tree.reduce();
+            let want = want.parse()?;
+            assert_eq!(tree, want, "\nInput {} Got {} Want {}", input, tree, want);
+        }
+        Ok(())
+    }
+    #[test]
+    fn test_explode() -> Result<()> {
+        for (input, want) in [
+            ("[[[[0,0],0],0],0]", "[[[[0,0],0],0],0]"),
+            ("[[[0,0],0],0]", "[[[0,0],0],0]"),
+            ("[[0,0],0]", "[[0,0],0]"),
+            ("[0,[0,[0,[0,0]]]]", "[0,[0,[0,[0,0]]]]"),
+            ("[0,[0,[0,0]]]", "[0,[0,[0,0]]]"),
+            ("[0,[0,0]]", "[0,[0,0]]"),
+            ("[[[[[9,8],1],2],3],4]", "[[[[0,9],2],3],4]"),
+            ("[7,[6,[5,[4,[3,2]]]]]", "[7,[6,[5,[7,0]]]]"),
+            ("[[6,[5,[4,[3,2]]]],1]", "[[6,[5,[7,0]]],3]"),
+            (
+                "[[3,[2,[1,[7,3]]]],[6,[5,[4,[3,2]]]]]",
+                "[[3,[2,[8,0]]],[9,[5,[4,[3,2]]]]]",
+            ),
+            (
+                "[[3,[2,[8,0]]],[9,[5,[4,[3,2]]]]]",
+                "[[3,[2,[8,0]]],[9,[5,[7,0]]]]",
+            ),
+        ] {
+            println!("== test_explode: {}", input);
+            let mut tree: Tree = input.parse()?;
+            tree.explode();
+            let want = want.parse()?;
+            assert_eq!(tree, want, "\nInput {} Got {} Want {}", input, tree, want);
+        }
+        Ok(())
+    }
+
+    #[test]
+    fn test_split() -> Result<()> {
+        for (input, want) in [
+            ("[10,0]", "[[5,5],0]"), //
+            ("[0,11]", "[0,[5,6]]"),
+            ("[[0,11],0]", "[[0,[5,6]],0]"),
+            ("[11,0]", "[[5,6],0]"),
+            ("[0,[11,0]]", "[0,[[5,6],0]]"),
+            ("[12,0]", "[[6,6],0]"),
+            ("[0,12]", "[0,[6,6]]"),
+        ] {
+            println!("== test_split: {}", input);
+            let mut tree: Tree = input.parse()?;
+            dbg!(&tree);
+            tree.split();
+            let want = want.parse()?;
+            assert_eq!(tree, want, "\nInput {} Got {} Want {}", input, tree, want);
+        }
+        Ok(())
+    }
+
+    #[test]
+    fn test_magnitude() -> Result<()> {
+        for (input, want) in [
+            ("[9,1]", 29),
+            ("[1,9]", 21),
+            ("[[9,1],[1,9]]", 129),
+            ("[[1,2],[[3,4],5]]", 143),
+            ("[[[[0,7],4],[[7,8],[6,0]]],[8,1]]", 1384),
+            ("[[[[1,1],[2,2]],[3,3]],[4,4]]", 445),
+            ("[[[[3,0],[5,3]],[4,4]],[5,5]]", 791),
+            ("[[[[5,0],[7,4]],[5,5]],[6,6]]", 1137),
+            (
+                "[[[[8,7],[7,7]],[[8,6],[7,7]]],[[[0,7],[6,6]],[8,7]]]",
+                3488,
+            ),
+        ] {
+            let tree: Tree = input.parse()?;
+            assert_eq!(tree.magnitude(), want);
+        }
+        Ok(())
+    }
+
+    #[test]
+    fn test_add_and_reduce() -> Result<()> {
+        for (input, want) in [
+            (
+                r#"
+[1,1]
+[2,2]
+[3,3]
+[4,4]
+"#,
+                "[[[[1,1],[2,2]],[3,3]],[4,4]]",
+            ),
+            (
+                r#"
+[1,1]
+[2,2]
+[3,3]
+[4,4]
+[5,5]
+    "#
+                .trim(),
+                "[[[[3,0],[5,3]],[4,4]],[5,5]]",
+            ),
+            (
+                r#"
+[1,1]
+[2,2]
+[3,3]
+[4,4]
+[5,5]
+[6,6]
+    "#
+                .trim(),
+                "[[[[5,0],[7,4]],[5,5]],[6,6]]",
+            ),
+            (
+                r#"
+[[[[4,3],4],4],[7,[[8,4],9]]]
+[1,1]
+"#
+                .trim(),
+                "[[[[0,7],4],[[7,8],[6,0]]],[8,1]]",
+            ),
+        ] {
+            println!("== 1. test_add_and_reduce: {}", input);
+            let mut num = sum(input.trim());
+            println!("before reduce: {}", num);
+            num.reduce();
+            println!("after reduce: {}", num);
+            assert_eq!(num.to_string(), want);
+        }
+
+        for (l, r, eq) in [
+            (
+                "[[[[4,3],4],4],[7,[[8,4],9]]]",
+                "[1,1]",
+                "[[[[0,7],4],[[7,8],[6,0]]],[8,1]]",
+            ),
+            (
+                "[[[0,[4,5]],[0,0]],[[[4,5],[2,6]],[9,5]]]",
+                "[7,[[[3,7],[4,3]],[[6,3],[8,8]]]]",
+                "[[[[4,0],[5,4]],[[7,7],[6,0]]],[[8,[7,7]],[[7,9],[5,0]]]]",
+            ),
+            (
+                "[[[[4,0],[5,4]],[[7,7],[6,0]]],[[8,[7,7]],[[7,9],[5,0]]]]",
+                "[[2,[[0,8],[3,4]]],[[[6,7],1],[7,[1,6]]]]",
+                "[[[[6,7],[6,7]],[[7,7],[0,7]]],[[[8,7],[7,7]],[[8,8],[8,0]]]]",
+            ),
+            (
+                "[[[[6,7],[6,7]],[[7,7],[0,7]]],[[[8,7],[7,7]],[[8,8],[8,0]]]]",
+                "[[[[2,4],7],[6,[0,5]]],[[[6,8],[2,8]],[[2,1],[4,5]]]]",
+                "[[[[7,0],[7,7]],[[7,7],[7,8]]],[[[7,7],[8,8]],[[7,7],[8,7]]]]",
+            ),
+            (
+                "[[[[7,0],[7,7]],[[7,7],[7,8]]],[[[7,7],[8,8]],[[7,7],[8,7]]]]",
+                "[7,[5,[[3,8],[1,4]]]]",
+                "[[[[7,7],[7,8]],[[9,5],[8,7]]],[[[6,8],[0,8]],[[9,9],[9,0]]]]",
+            ),
+            (
+                "[[[[7,7],[7,8]],[[9,5],[8,7]]],[[[6,8],[0,8]],[[9,9],[9,0]]]]",
+                "[[2,[2,2]],[8,[8,1]]]",
+                "[[[[6,6],[6,6]],[[6,0],[6,7]]],[[[7,7],[8,9]],[8,[8,1]]]]",
+            ),
+            (
+                "[[[[6,6],[6,6]],[[6,0],[6,7]]],[[[7,7],[8,9]],[8,[8,1]]]]",
+                "[2,9]",
+                "[[[[6,6],[7,7]],[[0,7],[7,7]]],[[[5,5],[5,6]],9]]",
+            ),
+            (
+                "[[[[6,6],[7,7]],[[0,7],[7,7]]],[[[5,5],[5,6]],9]]",
+                "[1,[[[9,3],9],[[9,0],[0,7]]]]",
+                "[[[[7,8],[6,7]],[[6,8],[0,8]]],[[[7,7],[5,0]],[[5,5],[5,6]]]]",
+            ),
+            (
+                "[[[[7,8],[6,7]],[[6,8],[0,8]]],[[[7,7],[5,0]],[[5,5],[5,6]]]]",
+                "[[[5,[7,4]],7],1]",
+                "[[[[7,7],[7,7]],[[8,7],[8,7]]],[[[7,0],[7,7]],9]]",
+            ),
+            (
+                "[[[[7,7],[7,7]],[[8,7],[8,7]]],[[[7,0],[7,7]],9]]",
+                "[[[[4,2],2],6],[8,7]]",
+                "[[[[8,7],[7,7]],[[8,6],[7,7]]],[[[0,7],[6,6]],[8,7]]]",
+            ),
+        ] {
+            let l: Tree = l.parse()?;
+            let r: Tree = r.parse()?;
+            let mut num = l + r;
+            println!("== 2. test_add_and_reduce: {}", num);
+            println!("before reduce: {}", num);
+            num.reduce();
+            println!("after reduce: {}", num);
+            assert_eq!(num.to_string(), eq);
+        }
+        Ok(())
+    }
+
+    #[test]
+    fn test_part1() -> Result<()> {
+        let input = r#"
+[[[0,[4,5]],[0,0]],[[[4,5],[2,6]],[9,5]]]
+[7,[[[3,7],[4,3]],[[6,3],[8,8]]]]
+[[2,[[0,8],[3,4]]],[[[6,7],1],[7,[1,6]]]]
+[[[[2,4],7],[6,[0,5]]],[[[6,8],[2,8]],[[2,1],[4,5]]]]
+[7,[5,[[3,8],[1,4]]]]
+[[2,[2,2]],[8,[8,1]]]
+[2,9]
+[1,[[[9,3],9],[[9,0],[0,7]]]]
+[[[5,[7,4]],7],1]
+[[[[4,2],2],6],[8,7]]
+    "#
+        .trim();
+
+        assert_eq!(part1(input)?, 3488);
+
+        let input = r#"
+[[[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]]]
+    "#
+        .trim();
+        assert_eq!(part1(input)?, 4140);
+        Ok(())
+    }
+
+    /*
+    #[test]
+    fn test_part2()->Result<()> {
+    let input = r#"
+    "#
+    .trim();
+    assert_eq!(part2(input)?, usize::MAX);
+    Ok(())
+    }
+    */
+}

2021/src/lib.rs

@@ -7,6 +7,7 @@ pub mod day13;
 pub mod day15;
 pub mod day16;
 pub mod day17;
+pub mod day18;
 pub mod day2;
 pub mod day3;
 pub mod day4;

src/lib.rs

@@ -1,7 +1,7 @@
 pub mod prelude {
     pub use std::{
         convert::Infallible,
-        fmt::{Debug, Error, Formatter},
+        fmt::{Debug, Display, Error, Formatter},
         io::Read,
         num::ParseIntError,
         ops::{Index, IndexMut},