// 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.

//

// Runtime 1ms Beats 98.78%of users with Java

// Memory 43.72MB Beats 72.14%of users with Java

/**

* Definition for a binary tree node.

* public class TreeNode {

* int val;

* TreeNode left;

* TreeNode right;

* TreeNode() {}

* TreeNode(int val) { this.val = val; }

* TreeNode(int val, TreeNode left, TreeNode right) {

* this.val = val;

* this.left = left;

* this.right = right;

* }

* }

*/

class Solution {

public List<TreeNode> delNodes(TreeNode root, int[] to_delete) {

List<TreeNode> list = new ArrayList<>();

Set<Integer> set = new HashSet<>();

for (int val: to_delete) {

set.add(val);

}

traverse(root, set, list, null);

return list;

}

private void traverse(TreeNode cur, Set<Integer> set, List<TreeNode> list, TreeNode parent) {

if (cur == null) {

return;

}

traverse(cur.left, set, list, cur);

traverse(cur.right, set, list, cur);

if (set.contains(cur.val)) {

if (cur.left != null && !set.contains(cur.left.val)) {

list.add(cur.left);

}

if (cur.right != null && !set.contains(cur.right.val)) {

list.add(cur.right);

}

if (parent != null && cur == parent.left) {

parent.left = null;

} else if (parent != null && cur == parent.right) {

parent.right = null;

}

} else {

if (parent == null) {

list.add(cur);

}

}

}

}