199. Binary Tree Right Side View

Given a binary tree, imagine yourself standing on the right side of it, return the values of the nodes you can see ordered from top to bottom.

Example:

```Input: [1,2,3,null,5,null,4]
Output: [1, 3, 4]
Explanation:

1            <---
/   \
2     3         <---
\     \
5     4       <---
```

199. Binary Tree Right Side View
``````struct Solution;
use rustgym_util::*;

trait Preorder {
fn preorder(&self, level: usize, view: &mut Vec<i32>);
}

fn preorder(&self, level: usize, view: &mut Vec<i32>) {
if let Some(node) = self {
let node = node.borrow();
let val = node.val;
if level == view.len() {
view.push(val);
} else {
view[level] = val;
}
node.left.preorder(level + 1, view);
node.right.preorder(level + 1, view);
}
}
}

impl Solution {
fn right_side_view(root: TreeLink) -> Vec<i32> {
let mut res: Vec<i32> = vec![];
root.preorder(0, &mut res);
res
}
}

#[test]
fn test() {
let root = tree!(1, tree!(2, None, tree!(5)), tree!(3, None, tree!(4)));
let res = vec![1, 3, 4];
assert_eq!(Solution::right_side_view(root), res);
}
``````