Diameter of binary tree

Tree Depth-First Search Binary Tree

65.1% acceptance

Feb 19, 2026

15548

1235

Given the root of a binary tree, return the length of the diameter of the tree. The diameter of a binary tree is the length of the longest path between any two nodes in a tree. This path may or may not pass through the root. The length of a path between two nodes is represented by the number of edges between them.

Solution

Rust

Time O(n)

Space O(n)

LeetCode

solution.rs

// Definition for a binary tree node.
// #[derive(Debug, PartialEq, Eq)]
// pub struct TreeNode {
//   pub val: i32,
//   pub left: Option<Rc<RefCell<TreeNode>>>,
//   pub right: Option<Rc<RefCell<TreeNode>>>,
// }
// 
// impl TreeNode {
//   #[inline]
//   pub fn new(val: i32) -> Self {
//     TreeNode {
//       val,
//       left: None,
//       right: None
//     }
//   }
// }
use std::rc::Rc;
use std::cell::RefCell;
impl Solution {
  pub fn diameter_of_binary_tree(root: Option<Rc<RefCell<TreeNode>>>) -> i32 {
    let mut max_d = 0i32;
    fn depth(node: &Option<Rc<RefCell<TreeNode>>>, max_d: &mut i32) -> i32 {
      if let Some(n) = node {
        let nb = n.borrow();
        let l = depth(&nb.left, max_d);
        let r = depth(&nb.right, max_d);
        *max_d = (*max_d).max(l + r);
        1 + l.max(r)
      } else { 0 }
    }
    depth(&root, &mut max_d);
    max_d
  }
}