LeetCode - Binary Tree Level Order Traversal

Question

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,#,#,15,7},

 3
/ \
9  20
  /  \
 15   7

return its level order traversal as:

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

Code

一个比较挫的版本，用上了队列。（C++ : 8ms）

/** * Definition for a binary tree node. * struct TreeNode { * int val; * TreeNode *left; * TreeNode *right; * TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */
class Solution {
public:
    vector<vector<int>> levelOrder(TreeNode* root) {
        vector<vector<int>> result;
        if(root == NULL) return result;

        int len;
        queue<TreeNode*> q; 
        q.push(root);
        while(!q.empty()){
            len = q.size();
            vector<int> vet;
            for(int i = 0; i < len; i++){
                TreeNode *temp = q.front();
                vet.push_back(temp->val);
                if(temp->left != NULL) q.push(temp->left);
                if(temp->right != NULL) q.push(temp->right);
                q.pop();
            }
            result.push_back(vet);
        }
        return result;
    }
};