775. N-ary Tree Preorder Traversal

• Difficulty: Easy

• Topics: Tree

• Similar Questions:

  • Binary Tree Preorder Traversal

  • N-ary Tree Level Order Traversal

  • N-ary Tree Postorder Traversal

Problem:

Given an n-ary tree, return the preorder traversal of its nodes' values.

For example, given a 3-ary tree:

Return its preorder traversal as: [1,3,5,6,2,4].

Note:

Recursive solution is trivial, could you do it iteratively?

Solutions:

/*
// Definition for a Node.
class Node {
public:
    int val;
    vector<Node*> children;

    Node() {}

    Node(int _val, vector<Node*> _children) {
        val = _val;
        children = _children;
    }
};
*/
class Solution {
public:
    vector<int> preorder(Node* root) {
        vector<int> ret;
        helper(root, ret);
        return ret;
    }

private:
    void helper(Node* root, vector<int>& ret) {
        if (root == nullptr)    return;
        ret.push_back(root->val);
        for (auto& child : root->children) {
            helper(child, ret);
        }
    }

};