(N叉树 BFS) leetcode429. N-ary Tree Level Order Traversal

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]
]

Note:

1. The depth of the tree is at most 1000.
2. The total number of nodes is at most 5000.

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这个层序遍历，自然用BFS写。和二叉树的层序遍历类似，连代码不会相差很大。

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 {};
        queue<Node*> q;
        q.push(root);
        vector<vector<int> > vec;
        while(!q.empty()){
            vector<int> vec1;
            int ans = q.size();
            for(int i = ans;i > 0; i--){
                auto t = q.front();
                q.pop();
                vec1.push_back(t->val);
                for(Node *cur:t->children){
                    q.push(cur);
                }
            }
            vec.push_back(vec1);
        }
        return vec;
    }
};