Delete Nodes And Return Forest

给一个数, 给一个数组, 删除树上的数组的节点. 然后返回删除后的森林(不连接的节点)

这题注意的是删完后要看下是否有root….

/**
 * 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> res = new ArrayList<>();
        Set<Integer> d = new HashSet<>();
        for(int n: to_delete)
            d.add(n);
        if(!d.contains(root.val))
            res.add(root);
        inorder(res, root, d);
        return res;
    }
    
    public TreeNode inorder(List<TreeNode> res, TreeNode root, Set<Integer> d){
        if(root == null)
            return null;
        root.left = inorder(res, root.left, d);
        root.right = inorder(res, root.right, d);
        if(d.contains(root.val)){
            d.remove(root.val);
            if(root.left != null)
                res.add(root.left);
            if(root.right != null)
                res.add(root.right);
            return null;
        }
        return root;
    }
}