1110. Delete Nodes And Return Forest

Given the `root` of a binary tree, each node in the tree has a distinct value.

After deleting all nodes with a value in `to_delete`, we are left with a forest (a disjoint union of trees).

Return the roots of the trees in the remaining forest. You may return the result in any order.

Example 1:

```Input: root = [1,2,3,4,5,6,7], to_delete = [3,5]
Output: [[1,2,null,4],[6],[7]]
```

Example 2:

```Input: root = [1,2,4,null,3], to_delete = [3]
Output: [[1,2,4]]
```

Constraints:

• The number of nodes in the given tree is at most `1000`.
• Each node has a distinct value between `1` and `1000`.
• `to_delete.length <= 1000`
• `to_delete` contains distinct values between `1` and `1000`.

1110. Delete Nodes And Return Forest
``````struct Solution;
use rustgym_util::*;
use std::collections::HashSet;
use std::iter::FromIterator;

trait Postorder {
fn postorder(self, nodes: &HashSet<i32>) -> (TreeLink, Vec<TreeLink>);
}

impl Postorder for TreeLink {
fn postorder(self, nodes: &HashSet<i32>) -> (TreeLink, Vec<TreeLink>) {
if let Some(node) = self {
let val = node.borrow_mut().val;
let left = node.borrow_mut().left.take();
let right = node.borrow_mut().right.take();
let (left_root, left_forest) = left.postorder(nodes);
let (right_root, right_forest) = right.postorder(nodes);
let mut forest = vec![];
for t in left_forest {
forest.push(t);
}
for t in right_forest {
forest.push(t);
}
if nodes.contains(&val) {
if left_root.is_some() {
forest.push(left_root);
}
if right_root.is_some() {
forest.push(right_root);
}
(None, forest)
} else {
node.borrow_mut().left = left_root;
node.borrow_mut().right = right_root;
(Some(node), forest)
}
} else {
(None, vec![])
}
}
}

impl Solution {
fn del_nodes(root: TreeLink, to_delete: Vec<i32>) -> Vec<TreeLink> {
let nodes = HashSet::from_iter(to_delete);
let mut res = vec![];
let (root, forest) = root.postorder(&nodes);
if root.is_some() {
res.push(root);
}
for t in forest {
res.push(t);
}
res
}
}

#[test]
fn test() {
let root = tree!(
1,
tree!(2, tree!(4), tree!(5)),
tree!(3, tree!(6), tree!(7))
);
let to_delete = vec![3, 5];
let res = vec![tree!(1, tree!(2, tree!(4), None), None), tree!(6), tree!(7)];
assert_eq!(Solution::del_nodes(root, to_delete), res);
}
``````