102. Binary Tree Level Order Traversal

/** * 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) {        queue<TreeNode *> q;        q.push(root);        vector<vector<int>> ret;         if(!root)return ret;        while(!q.empty())        {            int n=q.size();            vector<int> temp;            temp.clear();            for(int i=0;i<n;i++)            {                TreeNode *f=q.front();                temp.push_back(f->val);                q.pop();                if(f->left)                {                    q.push(f->left);                }                if(f->right)                {                    q.push(f->right);                }            }            ret.push_back(temp);        }        return ret;    }};