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path: root/binary_tree_preorder.rs
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use std::rc::Rc;
use std::cell::RefCell;
#[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
        }
    }
}

struct Solution;

impl Solution {
    pub fn preorder_traversal(root: Option<Rc<RefCell<TreeNode>>>) -> Vec<i32> {
        let mut ans: Vec<i32> = Vec::new();
        let mut stack: Vec<Option<Rc<RefCell<TreeNode>>>> = vec![root];
        while let Some(last) = stack.pop() {
            if let Some(n) = last {
                ans.push(n.borrow().val);
                stack.push(n.borrow().right.clone());
                stack.push(n.borrow().left.clone());
            }
        }
        ans
    }
}