107. Binary Tree Level Order Traversal II

class Solution {public:    queue<TreeNode*> q;    stack<vector<int>*> s;    vector<vector<int>> ans;    vector<vector<int>> levelOrderBottom(TreeNode* root) {        if(!root)            return ans;        q.push(root);        while(!q.empty()){            int sz = q.size();            vector<int> *temp = new vector<int>();            while(sz--){                TreeNode *p = q.front();                q.pop();                temp->push_back(p->val);                if(p->left) q.push(p->left);                if(p->right) q.push(p->right);            }            s.push(temp);        }        while(!s.empty()){            ans.push_back(*s.top());            s.pop();        }        return ans;    }};