Binary Tree Level Order Traversal II --leetcode C++

class Solution {
public:
    vector<vector<int> > levelOrderBottom(TreeNode* root) {
        vector<vector<int> >vec;
        if(root==NULL){
            return vec;
        }
        queue <TreeNode *>qu;
        qu.push(root);
        int count=1;//保存每一层的节点数量

        while(!qu.empty()){
            vector <int> v;
            while(count>=0){
                TreeNode *node;

                node=qu.front();
                qu.pop();
                v.push_back(node->val);
                count--;
                if(node->left!=NULL){
                    qu.push(node->left);
                }
                if(node->right!=NULL){
                    qu.push(node->right);
                }
            }
            vec.insert(vec.begin(),v);
            count=qu.size();
        }

    }
};