429. N-ary Tree Level Order Traversal ------------M

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

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

 

Example 1:

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

Example 2:

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

 

Constraints:

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

 

A:

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

    Node() {}

    Node(int _val) {
        val = _val;
    }

    Node(int _val, vector<Node*> _children) {
        val = _val;
        children = _children;
    }
};
*/

class Solution {
public:
    vector<vector<int>> levelOrder(Node* root) {
        vector<vector<int>> res;
        vector<Node*> curLevel;
        if(root){
            curLevel.push_back(root);
            res.push_back(vector<int>{root->val});
        }
        while(not curLevel.empty()){
            vector<Node*> next;
            vector<int> nextLevel;
            for(int i =0;i<curLevel.size();i++){
                auto ptr = curLevel[i];
                for(auto & tmp : ptr->children){
                    next.push_back(tmp);
                    nextLevel.push_back(tmp->val);
                }
            }
            if(not nextLevel.empty())
                res.push_back(nextLevel);
            curLevel = next;
        }
        return res;
    }
};

Error：

最后忘了检查nextLevel是否为空。  TNND