Rust - Leetcode - Easy - Sum of left leaves

rust-sum-of-left-leaves.rs

// Leetcode problem: https://leetcode.com/problems/sum-of-left-leaves/
// Easy but difficult when Rust's Rc<RefCell<T>> is used for rust beginners

// 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_of_left_leaves(root: Option<Rc<RefCell<TreeNode>>>) -> i32 {
        fn inner_sum(node: Option<Rc<RefCell<TreeNode>>>, is_left: bool) -> i32 {
            let mut sum: i32 = 0;
            if let Some(node_val) = node {
                let inner_node = node_val.borrow();
                if inner_node.left.is_none() && inner_node.right.is_none() {
                    if is_left {
                        sum += inner_node.val;
                    }
                }
                if let Some(left) = &inner_node.left {
                    sum += inner_sum(Some(left.clone()), true);
                }
                if let Some(right) = &inner_node.right {
                    sum += inner_sum(Some(right.clone()), false);
                }
            }

            sum
        }
        inner_sum(root, false)
    }
}