Binary Tree Level Order Traversal

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]]

此题主要是广度搜索，主要考基础，注意细节即可。

vector<vector<int> > levelOrder(TreeNode *root) {                if(root == NULL) return vector<vector<int> >();                vector<vector<int> >  res;        vector<int> res_one;        vector<TreeNode *> parent,chlid;//一个存放父节点，一个存放子节点        parent.push_back(root);                while(parent.size() > 0)        {            for(int i = 0;i < parent.size();i++)            {                res_one.push_back(parent[i]->val);                                if(parent[i]->left)                {                    chlid.push_back(parent[i]->left);                }                if(parent[i]->right)                {                    chlid.push_back(parent[i]->right);                }            }            res.push_back(res_one);            parent = chlid;//容器可以直接赋值。            chlid.clear();            res_one.clear();//清除结果，进行下一次        }        return res;    }