LeetCode 102. Binary Tree Level Order Traversal

问题描述：

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]]

AC代码如下：

vector<vector<int>> levelOrder(TreeNode* root)     {        vector<vector<int> >res;//结果数组        if(root == NULL)            return res;        queue<TreeNode*>Queue;        Queue.push(root);        while(Queue.size() > 0)        {            vector<int>row;//每一行            queue<TreeNode*>temp;            while(Queue.size() > 0)            {                TreeNode * node = Queue.front();                Queue.pop();                if(node->left != NULL)                    temp.push(node->left);                if(node->right != NULL)                    temp.push(node->right);                row.push_back(node->val);            }            Queue = temp;            res.push_back(row);        }        return res;    }