Formatted question description: https://leetcode.ca/all/1490.html

1490. Clone N-ary Tree

Level

Medium

Description

Given a root of an N-ary tree, return a deep copy (clone) of the tree.

Each node in the n-ary tree contains a val (int) and a list (List[Node]) of its children.

class Node {
    public int val;
    public List<Node> children;
}

Nary-Tree input serialization is represented in their level order traversal, each group of children is separated by the null value (See examples).

Follow up: Can your solution work for the graph problem?

Example 1:

Image text

Input: root = [1,null,3,2,4,null,5,6]

Output: [1,null,3,2,4,null,5,6]

Example 2:

Image text

Input: root = [1,null,2,3,4,5,null,null,6,7,null,8,null,9,10,null,null,11,null,12,null,13,null,null,14]

Output: [1,null,2,3,4,5,null,null,6,7,null,8,null,9,10,null,null,11,null,12,null,13,null,null,14]

Constraints:

  • The depth of the n-ary tree is less than or equal to 1000.
  • The total number of nodes is between [0, 10^4].

Solution

Use recursion to do the cloning. If root is null, then return null. Otherwise, clone a new root from root, and do the cloning for each child of root and assign the cloned children to the new root. Finally, return the new root.

  • /*
    // Definition for a Node.
    class Node {
        public int val;
        public List<Node> children;
    
        
        public Node() {
            children = new ArrayList<Node>();
        }
        
        public Node(int _val) {
            val = _val;
            children = new ArrayList<Node>();
        }
        
        public Node(int _val,ArrayList<Node> _children) {
            val = _val;
            children = _children;
        }
    };
    */
    
    class Solution {
        public Node cloneTree(Node root) {
            if (root == null)
                return root;
            Node newRoot = new Node(root.val);
            List<Node> children = root.children;
            for (Node child : children) {
                Node newChild = cloneTree(child);
                newRoot.children.add(newChild);
            }
            return newRoot;
        }
    }
    
  • // OJ: https://leetcode.com/problems/clone-n-ary-tree/
    // Time: O(N)
    // Space: O(H)
    class Solution {
    public:
        Node* cloneTree(Node* root) {
            if (!root) return nullptr;
            auto cpy = new Node(root->val);
            for (auto &c : root->children) cpy->children.push_back(cloneTree(c));
            return cpy;
        }
    };
    
  • print("Todo!")
    

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