Day 18 basic parse/Display implementations.

2021/src/day18.rs

@@ -0,0 +1,232 @@
+use advent::prelude::*;
+use aoc_runner_derive::{aoc, aoc_generator};
+use std::io::Read;
+
+#[derive(Debug, PartialEq)]
+enum ChildType {
+    None,
+    Value(usize),
+    Subtree(Idx),
+}
+
+#[derive(Copy, Clone, Debug, Default, PartialEq)]
+struct Idx(usize);
+
+#[derive(Debug, PartialEq)]
+struct Node {
+    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, PartialEq)]
+struct Tree {
+    root: Idx,
+    nodes: Vec<Node>,
+}
+
+fn read_byte<R: Read>(reader: &mut R) -> std::io::Result<Option<u8>> {
+    reader.bytes().next().transpose()
+}
+
+impl Tree {
+    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 {
+            idx,
+            parent: None,
+            left,
+            right,
+        });
+        idx
+    }
+
+    fn from_str_node<R: Read>(&mut self, r: &mut R) -> 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 v = dbg!(b - b'0');
+                    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(())
+    }
+}
+
+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'[')
+        );
+        tree.from_str_node(&mut bytes);
+        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(())
+    }
+}
+
+#[aoc(day18, part1)]
+fn part1(input: &str) -> Result<usize> {
+    for l in input.lines() {
+        let tree: Tree = l.parse()?;
+        dbg!(&tree);
+    }
+    Ok(0)
+}
+
+/*
+#[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_part1() -> Result<()> {
+        let sum = [
+            [[[6, 6], [7, 6]], [[7, 7], [7, 0]]],
+            [[[7, 7], [7, 7]], [[7, 8], [9, 9]]],
+        ];
+        dbg!(&sum);
+        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;