DSA-Java-Leetcode/1110. Delete Nodes And Return Forest at main · risitadas/DSA-Java-Leetcode · GitHub

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/**
 * 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
{
    ArrayList<TreeNode> result = new ArrayList<>();
    boolean[] toDeleteSet = new boolean[1001];


    public List<TreeNode> delNodes(TreeNode root, int[] to_delete)
    {
        for(int n : to_delete)
        {
            toDeleteSet[n] = true;
        }
        dfs(root, true);
        return result;

    }

    public TreeNode dfs(TreeNode root, boolean isRoot) // boolean flag
    {
        if(root == null) return root;

        root.left = dfs(root.left, toDeleteSet[root.val]);
        root.right = dfs(root.right, toDeleteSet[root.val]);

        if(!toDeleteSet[root.val] && isRoot)
        {
            result.add(root);

        }

        return toDeleteSet[root.val] ? null : root;


    }


}