Closest binary search tree value

Binary Search Tree Depth-First Search Binary Search Tree Binary Tree

49.2% acceptance

Mar 31, 2026

1902

166

Given the root of a binary search tree and a target value, return the value in the BST that is closest to the target. If there are multiple answers, print the smallest.

Solution

Rust

Time O(n)

Space O(1)

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 closest_value(root: Option<Rc<RefCell<TreeNode>>>, target: f64) -> i32 {
    let mut closest = root.as_ref().unwrap().borrow().val;
    let mut node = root;
    while let Some(n) = node {
      let n_ref = n.borrow();
      let val = n_ref.val;
      if (val as f64 - target).abs() < (closest as f64 - target).abs()
        || ((val as f64 - target).abs() == (closest as f64 - target).abs() && val < closest)
      {
        closest = val;
      }
      node = if target < val as f64 {
        n_ref.left.clone()
      } else {
        n_ref.right.clone()
      };
    }
    closest
  }
}