Binary Tree Level Order Traversal ii

class Solution {
public:
    vector<vector<int>> levelOrderBottom(TreeNode* root) {
           if(root==NULL)return {};
        vector<vector<int>> ans;

        queue<TreeNode*> q;
        q.push(root);

        while(q.size()!=0){

            int n = q.size();

            vector<int> v;
            for(int i = 0; i<n; i++){

                TreeNode * temp = q.front();
                q.pop();
                v.push_back(temp->val);
                if(temp->left!=NULL){
                    q.push(temp->left);
                }
                if(temp->right!=NULL){
                    q.push(temp->right);
                }

            }

            ans.push_back(v);

        }
        reverse(ans.begin(),ans.end());
        return ans;
    }
};