树————N叉树的层序遍历

思想：

使用队的思想，将每一层的节点放入队列中，依次弹出，同时将其children放入队列。

c++

 1 /*
 2 // Definition for a Node.
 3 class Node {
 4 public:
 5     int val;
 6     vector<Node*> children;
 7 
 8     Node() {}
 9 
10     Node(int _val, vector<Node*> _children) {
11         val = _val;
12         children = _children;
13     }
14 };
15 */
16 class Solution {
17 private:
18     vector<vector<int> > res;
19     vector<int> small_res;
20     queue<Node*> que;    
21 public:
22     vector<vector<int>> levelOrder(Node* root) {
23         if(!root) return res;
24         que.push(root);
25         while(!que.empty()){
26             small_res.erase(small_res.begin(),small_res.end());
27             int s=que.size();
28             for(int i=0;i<s;i++){
29                 Node *temp=que.front();
30                 que.pop();
31                 small_res.push_back(temp->val);
32                 if(!temp->children.empty()){
33                     for(Node* child: temp->children){
34                         que.push(child);
35                     }
36                 }
37             }
38             res.push_back(small_res);
39         }
40         
41         return res;
42     }
43 };

或者：（做了一些小改动）

 1 /*
 2 // Definition for a Node.
 3 class Node {
 4 public:
 5     int val;
 6     vector<Node*> children;
 7 
 8     Node() {}
 9 
10     Node(int _val, vector<Node*> _children) {
11         val = _val;
12         children = _children;
13     }
14 };
15 */
16 class Solution {
17 public:
18     vector<vector<int>> levelOrder(Node* root) {
19         vector<int>v1;
20         vector<vector<int>>v2;
21         if(root==NULL) return v2;
22         queue<Node*>q;
23         q.push(root);
24         while(!q.empty()){
25             int cnt=q.size();
26             v1.clear();
27             while(cnt--){
28               Node *tmp=q.front();
29               v1.push_back(tmp->val);
30               q.pop();
31               for(int i=0;i<tmp->children.size();i++){
32                   q.push(tmp->children[i]);
33               }
34             }
35             v2.push_back(v1);
36         }
37         return v2;
38     }
39 };