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;
}
};
