## 563. Binary Tree Tilt

Given the `root`

of a binary tree, return *the sum of every tree node's tilt.*

The **tilt** of a tree node is the **absolute difference** between the sum of all left subtree node **values** and all right subtree node **values**. If a node does not have a left child, then the sum of the left subtree node **values** is treated as `0`

. The rule is similar if there the node does not have a right child.

**Example 1:**

Input:root = [1,2,3]Output:1Explanation:Tilt of node 2 : |0-0| = 0 (no children) Tilt of node 3 : |0-0| = 0 (no children) Tile of node 1 : |2-3| = 1 (left subtree is just left child, so sum is 2; right subtree is just right child, so sum is 3) Sum of every tilt : 0 + 0 + 1 = 1

**Example 2:**

Input:root = [4,2,9,3,5,null,7]Output:15Explanation:Tilt of node 3 : |0-0| = 0 (no children) Tilt of node 5 : |0-0| = 0 (no children) Tilt of node 7 : |0-0| = 0 (no children) Tilt of node 2 : |3-5| = 2 (left subtree is just left child, so sum is 3; right subtree is just right child, so sum is 5) Tilt of node 9 : |0-7| = 7 (no left child, so sum is 0; right subtree is just right child, so sum is 7) Tilt of node 4 : |(3+5+2)-(9+7)| = |10-16| = 6 (left subtree values are 3, 5, and 2, which sums to 10; right subtree values are 9 and 7, which sums to 16) Sum of every tilt : 0 + 0 + 0 + 2 + 7 + 6 = 15

**Example 3:**

Input:root = [21,7,14,1,1,2,2,3,3]Output:9

**Constraints:**

- The number of nodes in the tree is in the range
`[0, 10`

.^{4}] `-1000 <= Node.val <= 1000`

## Rust Solution

```
struct Solution;
use rustgym_util::*;
trait Tilt {
fn find_tilt(&self, tilt: &mut i32) -> i32;
}
impl Tilt for TreeLink {
fn find_tilt(&self, tilt: &mut i32) -> i32 {
if let Some(node) = self {
let node = node.borrow();
let left = &node.left;
let right = &node.right;
let left_sum = left.find_tilt(tilt);
let right_sum = right.find_tilt(tilt);
*tilt += (left_sum - right_sum).abs();
node.val + left_sum + right_sum
} else {
0
}
}
}
impl Solution {
fn find_tilt(root: TreeLink) -> i32 {
let mut tilt = 0;
root.find_tilt(&mut tilt);
tilt
}
}
#[test]
fn test() {
let root = tree!(1, tree!(2), tree!(3));
assert_eq!(Solution::find_tilt(root), 1);
}
```

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