965. Univalued Binary Tree

A binary tree is univalued if every node in the tree has the same value.

Return `true` if and only if the given tree is univalued.

Example 1:

```Input: [1,1,1,1,1,null,1]
Output: true
```

Example 2:

```Input: [2,2,2,5,2]
Output: false
```

Note:

1. The number of nodes in the given tree will be in the range `[1, 100]`.
2. Each node's value will be an integer in the range `[0, 99]`.

965. Univalued Binary Tree
``````struct Solution;
use rustgym_util::*;

trait Preorder {
fn is_unival(&self) -> bool;
fn preorder(&self, val: &mut Option<i32>) -> bool;
}

fn is_unival(&self) -> bool {
let mut val: Option<i32> = None;
self.preorder(&mut val)
}
fn preorder(&self, val: &mut Option<i32>) -> bool {
if let Some(node) = self {
let node = node.borrow();
let node_val = node.val;
if let Some(val) = val {
if *val != node_val {
return false;
}
} else {
*val = Some(node_val);
}
node.left.preorder(val) && node.right.preorder(val)
} else {
true
}
}
}

impl Solution {
fn is_unival_tree(root: TreeLink) -> bool {
root.is_unival()
}
}

#[test]
fn test() {
let root = tree!(1, tree!(1, tree!(1), tree!(1)), tree!(1, None, tree!(1)));
assert_eq!(Solution::is_unival_tree(root), true);
let root = tree!(2, tree!(2, tree!(5), tree!(2)), tree!(2));
assert_eq!(Solution::is_unival_tree(root), false);
}
``````