102. Binary Tree Level Order Traversal

   

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• Difficulty: Medium
• Contributors: Admin

 

Given a binary tree, return the level order traversal of its nodes' values. (ie, from left to right, level by level).

For example:

Given binary tree [3,9,20,null,null,15,7],

3   / \  9  20    /  \   15   7

 

return its level order traversal as:

[  [3],  [9,20],  [15,7]]

 

 

1 /** 2  * Definition for a binary tree node. 3  * struct TreeNode { 4  *     int val; 5  *     TreeNode *left; 6  *     TreeNode *right; 7  *     TreeNode(int x) : val(x), left(NULL), right(NULL) {} 8  * }; 9  */10 class Solution {11 public:12     vector
          
           
            > levelOrder(TreeNode* root) {13         vector
            
             
              > res;14         if(!root) return res;15         queue
              
                q;16         q.push(root);17         while(!q.empty()){18             int size = q.size();19             vector
               
                 level;20 //level.clear();21 for(int i = 0; i < size; i++){22 //vector
                
                  level;23 TreeNode* tmp = q.front();24 q.pop();25 level.push_back(tmp -> val);26 if(tmp -> left){27 q.push(tmp -> left);28 }29 if(tmp -> right){30 q.push(tmp -> right);31 }32 }33 res.push_back(level);34 }35 return res;36 }37 };