1110 - Delete Nodes And Return Forest

JAVA

class Solution {
    private boolean[] s = new boolean[1001];
    private List<TreeNode> ans = new ArrayList<>();

    public List<TreeNode> delNodes(TreeNode root, int[] to_delete) {
        for (int x : to_delete) {
            s[x] = true;
        }
        if (dfs(root) != null) {
            ans.add(root);
        }
        return ans;
    }

    private TreeNode dfs(TreeNode root) {
        if (root == null) {
            return null;
        }
        root.left = dfs(root.left);
        root.right = dfs(root.right);
        if (!s[root.val]) {
            return root;
        }
        if (root.left != null) {
            ans.add(root.left);
        }
        if (root.right != null) {
            ans.add(root.right);
        }
        return null;
    }
}

C++

class Solution {
public:
    vector<TreeNode*> delNodes(TreeNode* root, vector<int>& to_delete) {
        bool s[1001];
        memset(s, 0, sizeof(s));
        for (int x : to_delete) {
            s[x] = true;
        }
        vector<TreeNode*> ans;
        function<TreeNode*(TreeNode*)> dfs = [&](TreeNode* root) -> TreeNode* {
            if (!root) {
                return nullptr;
            }
            root->left = dfs(root->left);
            root->right = dfs(root->right);
            if (!s[root->val]) {
                return root;
            }
            if (root->left) {
                ans.push_back(root->left);
            }
            if (root->right) {
                ans.push_back(root->right);
            }
            return nullptr;
        };
        if (dfs(root)) {
            ans.push_back(root);
        }
        return ans;
    }
};