Binary Tree Right Side View
<p>Given the <code>root</code> of a binary tree, imagine yourself standing on the <strong>right side</strong> of it, return <em>the values of the nodes you can see ordered from top to bottom</em>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<div class="example-block">
<p><strong>Input:</strong> <span class="example-io">root = [1,2,3,null,5,null,4]</span></p>

<p><strong>Output:</strong> <span class="example-io">[1,3,4]</span></p>

<p><strong>Explanation:</strong></p>

<p><img alt="" src="https://fastly.jsdelivr.net/gh/doocs/leetcode@main/solution/0100-0199/0199.Binary%20Tree%20Right%20Side%20View/images/tmpd5jn43fs-1.png" style="width: 400px; height: 207px;" /></p>
</div>

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

<div class="example-block">
<p><strong>Input:</strong> <span class="example-io">root = [1,2,3,4,null,null,null,5]</span></p>

<p><strong>Output:</strong> <span class="example-io">[1,3,4,5]</span></p>

<p><strong>Explanation:</strong></p>

<p><img alt="" src="https://fastly.jsdelivr.net/gh/doocs/leetcode@main/solution/0100-0199/0199.Binary%20Tree%20Right%20Side%20View/images/tmpkpe40xeh-1.png" style="width: 400px; height: 214px;" /></p>
</div>

<p><strong class="example">Example 3:</strong></p>

<div class="example-block">
<p><strong>Input:</strong> <span class="example-io">root = [1,null,3]</span></p>

<p><strong>Output:</strong> <span class="example-io">[1,3]</span></p>
</div>

<p><strong class="example">Example 4:</strong></p>

<div class="example-block">
<p><strong>Input:</strong> <span class="example-io">root = []</span></p>

<p><strong>Output:</strong> <span class="example-io">[]</span></p>
</div>

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

<ul>
	<li>The number of nodes in the tree is in the range <code>[0, 100]</code>.</li>
	<li><code>-100 &lt;= Node.val &lt;= 100</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 right_side_view(root: Option<Rc<RefCell<TreeNode>>>) -> Vec<i32> {
        let mut ans = vec![];
        if root.is_none() {
            return ans;
        }
        let mut q = VecDeque::new();
        q.push_back(root);
        while !q.is_empty() {
            let k = q.len();
            ans.push(q[0].as_ref().unwrap().borrow().val);
            for _ in 0..k {
                if let Some(node) = q.pop_front().unwrap() {
                    let mut node = node.borrow_mut();
                    if node.right.is_some() {
                        q.push_back(node.right.take());
                    }
                    if node.left.is_some() {
                        q.push_back(node.left.take());
                    }
                }
            }
        }
        ans
    }
}
