## 515. Find Largest Value in Each Tree Row

Given the `root` of a binary tree, return an array of the largest value in each row of the tree (0-indexed).

Example 1:

```Input: root = [1,3,2,5,3,null,9]
Output: [1,3,9]
```

Example 2:

```Input: root = [1,2,3]
Output: [1,3]
```

Example 3:

```Input: root = [1]
Output: [1]
```

Example 4:

```Input: root = [1,null,2]
Output: [1,2]
```

Example 5:

```Input: root = []
Output: []
```

Constraints:

• The number of nodes in the tree will be in the range `[0, 104]`.
• `-231 <= Node.val <= 231 - 1`

## Rust Solution

``````struct Solution;
use rustgym_util::*;

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

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

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

#[test]
fn test() {
let root = tree!(1, tree!(3, tree!(5), tree!(3)), tree!(2, None, tree!(9)));
let res = vec![1, 3, 9];
assert_eq!(Solution::largest_values(root), res);
}
``````

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