Build a Binary Tree

Create a fixed seven-node binary tree and render its shape.

Algorithm

The canonical tree is 4(2(1,3),6(5,7)), so this Rust DSA implementation can be compared directly with the rest of the DSA track.

Basic Implementation

basic.rs

use std::collections::VecDeque;
struct Node { value: i32, left: Option<Box<Node>>, right: Option<Box<Node>> }
impl Node {
    fn new(value: i32) -> Self { Self { value, left: None, right: None } }
    fn with(value: i32, left: Node, right: Node) -> Self {
        Self { value, left: Some(Box::new(left)), right: Some(Box::new(right)) }
    }
}
fn render(node: &Option<Box<Node>>) -> String {
    match node {
        None => "_".to_string(),
        Some(n) => {
            if n.left.is_none() && n.right.is_none() { n.value.to_string() }
            else { format!("{}({},{})", n.value, render(&n.left), render(&n.right)) }
        }
    }
}
fn sample_tree() -> Option<Box<Node>> {
    Some(Box::new(Node::with(4, Node::with(2, Node::new(1), Node::new(3)), Node::with(6, Node::new(5), Node::new(7)))))
}
fn list_string(values: &[i32]) -> String {
    format!("[{}]", values.iter().map(|v| v.to_string()).collect::<Vec<_>>().join(", "))
}
fn main() { let root = sample_tree(); println!("{}", render(&root)); }

Complexity

Time: O(n)
Space: O(n)

Implementation notes

Render tree structure explicitly instead of printing node objects.
The replay highlights the node, traversal state, queue, path, or search cursor that changes at each step.

node links A node stores one value plus references to its left and right children.