Sum root to leaf numbers

Tree Depth-First Search Binary Tree

69.6% acceptance

Feb 27, 2026

8633

158

You are given the root of a binary tree containing digits from 0 to 9 only. Each root-to-leaf path in the tree represents a number. For example, the root-to-leaf path 1 -> 2 -> 3 represents the number 123. Return the total sum of all root-to-leaf numbers. Test cases are generated so that the answer will fit in a 32-bit integer. A leaf node is a node with no children.

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 sum_numbers(root: Option<Rc<RefCell<TreeNode>>>) -> i32 {
    Self::sum_dfs(&root, 0)
  }
  
  fn sum_dfs(node: &Option<Rc<RefCell<TreeNode>>>, current: i32) -> i32 {
    if let Some(n) = node {
      let n = n.borrow();
      let val = current * 10 + n.val;
      
      if n.left.is_none() && n.right.is_none() {
        return val;
      }
      
      Self::sum_dfs(&n.left, val) + Self::sum_dfs(&n.right, val)
    } else {
      0
    }
  }
}