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;    }};