[每日 LeetCode] 429. N-ary Tree Level Order Traversal

原文链接 [每日 LeetCode] 429. N-ary Tree Level Order Traversal

Description:

Given an n-ary tree, return the level order traversal of its nodes' values. (ie, from left to right, level by level).

For example, given a 3-ary tree:

We should return its level order traversal:

[
     [1],
     [3,2,4],
     [5,6]
]
​

思路：本题和[每日 LeetCode] 102. Binary Tree Level Order Traversal 思想类似，不同之处在于对某个结点的孩子入队时遍历其孩子结点，并以此入队即可。

C++ 代码

/*
// 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<vector<int>> levelOrder(Node* root) {
        if(!root)
            return {};
        vector<vector<int>> res;
        queue<Node*> q{{root}};
        while(!q.empty()){
            vector<int> oneLevel;
            for (int i=q.size(); i>0; i--){
                Node* t = q.front();
                oneLevel.push_back(t->val);
                q.pop();
                if (!t->children.empty()){
                    for (auto a : t->children)
                        q.push(a);
                }
            }
            res.push_back(oneLevel);
        }
        return res;
    }
};
​

运行时间：156ms

运行时间：34M