Find Largest Value in Each Tree Row
<p>Given the <code>root</code> of a binary tree, return <em>an array of the largest value in each row</em> of the tree <strong>(0-indexed)</strong>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<img alt="" src="https://fastly.jsdelivr.net/gh/doocs/leetcode@main/solution/0500-0599/0515.Find%20Largest%20Value%20in%20Each%20Tree%20Row/images/largest_e1.jpg" style="width: 300px; height: 172px;" />
<pre>
<strong>Input:</strong> root = [1,3,2,5,3,null,9]
<strong>Output:</strong> [1,3,9]
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> root = [1,2,3]
<strong>Output:</strong> [1,3]
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li>The number of nodes in the tree will be in the range <code>[0, 10<sup>4</sup>]</code>.</li>
	<li><code>-2<sup>31</sup> &lt;= Node.val &lt;= 2<sup>31</sup> - 1</code></li>
</ul>
Tree; Depth-First Search; Breadth-First Search; Binary Tree
// 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::cell::RefCell;
use std::collections::VecDeque;
use std::rc::Rc;
impl Solution {
    pub fn largest_values(root: Option<Rc<RefCell<TreeNode>>>) -> Vec<i32> {
        let mut ans = Vec::new();
        let mut q = VecDeque::new();
        if root.is_some() {
            q.push_back(root.clone());
        }
        while !q.is_empty() {
            let mut x = i32::MIN;
            for _ in 0..q.len() {
                let node = q.pop_front().unwrap();
                let node = node.as_ref().unwrap().borrow();
                x = x.max(node.val);
                if node.left.is_some() {
                    q.push_back(node.left.clone());
                }
                if node.right.is_some() {
                    q.push_back(node.right.clone());
                }
            }
            ans.push(x);
        }
        ans
    }
}
